Additive and application thereof

ABSTRACT

An additive is provided. The additive includes an additive molecule having a structure represented by formula (I): 
     
       
         
         
             
             
         
       
         
         
           
             wherein R 1 , A 1 , A 2 , Z 1 , K 1 , n 1 , and n 2  are defined as in the specification.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of Taiwan Patent Application No. 108102902, filed on Jan. 25, 2019, the entirety of which is incorporated by reference herein.

BACKGROUND Technical Field

The present disclosure relates to an additive, a liquid-crystal composition, and a liquid-crystal display device using the additive.

Description of the Related Art

Liquid-crystal display devices have been used in various applications, including personal computers, personal digital assistants (PDAs), mobile phones, televisions, and so on, because these devices have many advantages. These advantages include being light in weight, having low power consumption, and not emitting radiation.

In a liquid-crystal display device, the alignment of liquid-crystal molecules can be achieved with a polyimide film. Conventional liquid-crystal alignment layers are generally produced by coating a polyimide onto a substrate to form a film, and then mechanically rubbing it to form the desired liquid-crystal alignment groove on the surface of the polyimide film. However, after rubbing the alignment film, uneven alignment may occur, or serious brush marks may be produced. As a result, the product yield of the liquid-crystal display device is not good.

Furthermore, the procedure can also be simplified without an alignment layer. Therefore, manufacturers have begun to develop liquid-crystal display devices having no alignment layer. The liquid-crystal composition of such a liquid-crystal display device contains polar compounds, and the liquid-crystal molecules are vertically aligned by the function of the polar compounds. However, it is difficult for such polar compounds to be compatible with vertical alignment ability and a high voltage holding ratio. Furthermore, the stability of the alignment ability of such polar compounds also needs to be improved.

Accordingly, a liquid-crystal composition having excellent vertical alignment ability, a high voltage holding ratio, and a high stability of its alignment ability is still needed in this technical field.

BRIEF SUMMARY

In one embodiment of the present disclosure, an additive is provided. The additive includes an additive molecule having a structure represented by formula (I):

-   -   wherein, in formula (I),     -   R¹ represents fluorine, chlorine, hydrogen, a C₁-C₂₀ linear         alkyl group, a C₃-C₂₀ branched alkyl group, a C₁-C₂₀ linear         alkoxy group, or a C₃-C₂₀ branched alkoxy group, wherein the         C₁-C₂₀ linear alkyl group, the C₃-C₂₀ branched alkyl group, the         C₁-C₂₀ linear alkoxy group, or the C₃-C₂₀ branched alkoxy group         is unsubstituted or at least one —CH₂— of the C₁-C₂₀ linear         alkyl group, the C₃-C₂₀ branched alkyl group, the C₁-C₂₀ linear         alkoxy group, or the C₃-C₂₀ branched alkoxy group is substituted         by —C≡C—, —CH═CH—, —CF₂O—, —O—, —COO—, —OCO—, or —OOC—, and/or         at least one hydrogen atom of the C₁-C₂₀ linear alkyl group, the         C₃-C₂₀ branched alkyl group, the C₁-C₂₀ linear alkoxy group, or         the C₃-C₂₀ branched alkoxy group is substituted by a halogen         atom;     -   A¹ represents a 1,4-phenylene group, a 1,4-cyclohexylene group,         a benzofuran-2,5-diyl group, a 1,3-dioxane-2,5-diyl group, a         tetrahydropyran-2,5-diyl group, a divalent         dioxabicyclo[2.2.2]octylene group, a divalent         trioxabicyclo[2.2.2]octylene group, a         tetrahydronaphthalene-2,6-diyl group, a 1,3-cyclopentylene, a         1,3-cyclobutylene, or an indane-2,5-diyl group, wherein the         1,4-phenylene group, the 1,4-cyclohexylene group, the         tetrahydronaphthalene-2,6-diyl group, the 1,3-cyclopentylene,         the 1,3-cyclobutylene, or the indane-2,5-diyl group is         unsubstituted or at least one hydrogen atom of the 1,4-phenylene         group, the 1,4-cyclohexylene group, the         tetrahydronaphthalene-2,6-diyl group, the 1,3-cyclopentylene,         the 1,3-cyclobutylene, or the indane-2,5-diyl group is         substituted by a halogen atom, —CH₃, —CH₂CH₃, or a —CN group,         and/or at least one —CH₂— of the 1,4-phenylene group, the         1,4-cyclohexylene group, the tetrahydronaphthalene-2,6-diyl         group, the 1,3-cyclopentylene, the 1,3-cyclobutylene, or the         indane-2,5-diyl group is substituted by —O—, —N— or —S—, and         wherein the —O—, —N—, and —S— do not directly bond to one         another;     -   A² represents a 1,4-phenylene group, a 1,4-cyclohexylene group,         a benzofuran-2,5-diyl group, or an indane-2,5-diyl group,         wherein the 1,4-phenylene group, the 1,4-cyclohexylene group,         the benzofuran-2,5-diyl group, or the indane-2,5-diyl group is         unsubstituted or at least one hydrogen atom of the 1,4-phenylene         group, the 1,4-cyclohexylene group, the benzofuran-2,5-diyl         group, or the indane-2,5-diyl group is substituted by a halogen         atom, —CH₃, —CH₂CH₃, or a —CN group, and/or at least one —CH₂—         of the 1,4-phenylene group, the 1,4-cyclohexylene group, the         benzofuran-2,5-diyl group, or the indane-2,5-diyl group is         substituted by —O—, —N— or —S—, and wherein the —O—, —N—, and         —S— do not directly bond to one another;     -   Z¹ represents a single bond, a C₁-C₁₅ alkylene group, a C₁-C₁₅         alkyleneoxy group, —C≡C—, —CH═CH—, —CF₂O—, —OCF₂—, —COO—, —OCO—,         or —OOC—, and —CF₂—CF₂—, or —CF═CF—;     -   n¹ represents 1, 2, or 3, and when n¹ represents 2 or 3, the two         or more A¹ groups are identical to each other or different from         each other, and the two or more Z¹ groups are identical to each         other or different from each other;     -   n² represents 0 or 1; and     -   K¹ represents a structure represented by formula (Ia), formula         (Ib), or formula (Ic):

-   -   wherein, in formula (Ia), formula (Ib), and formula (Ic),     -   each of L¹, L², and L³ independently represents a single bond, a         C₁-C₁₅ linear alkylene group, a C₃-C₁₅ branched alkylene group,         a C₁-C₁₅ linear alkyleneoxy group, or a C₃-C₁₅ branched         alkyleneoxy group, wherein the C₁-C₁₅ linear alkylene group, the         C₃-C₁₅ branched alkylene group, the C₁-C₁₅ linear alkyleneoxy         group, or the C₃-C₁₅ branched alkyleneoxy group is unsubstituted         or at least one —CH₂— of the C₁-C₁₅ linear alkylene group, the         C₃-C₁₅ branched alkylene group, the C₁-C₅ linear alkyleneoxy         group, or the C₃-C₁₅ branched alkyleneoxy group is substituted         by —C≡C—, —CH═CH—, —CF₂O—, —SiR^(a) ₂—, —O—, —COO—, —OCO—, or         —OOC—, and/or at least one hydrogen atom of the C₁-C₁₅ linear         alkylene group, the C₃-C₁₅ branched alkylene group, the C₁-C₁₅         linear alkyleneoxy group, or the C₃-C₁₅ branched alkyleneoxy         group is substituted by a halogen atom, and wherein R^(a)         represents a C₁-C₁₀ linear alkyl group or a C₃-C₁₀ branched         alkyl group, and two R^(a) groups bonded to the same Si atom are         identical to each other or different from each other;     -   each of R², R³ and R⁴ independently represents fluorine,         chlorine, hydrogen, a C₁-C₁₀ linear alkyl group, a C₃-C₁₀         branched alkyl group, a C₁-C₁₀ linear alkoxy group, or a C₃-C₁₀         branched alkoxy group, wherein the C₁-C₁₀ linear alkyl group,         the C₃-C₁₀ branched alkyl group, the C₁-C₁₀ linear alkoxy group,         or the C₃-C₁₀ branched alkoxy group is unsubstituted or at least         one —CH₂— of the C₁-C₁₀ linear alkyl group, the C₃-C₁₀ branched         alkyl group, the C₁-C₁₀ linear alkoxy group, or the C₃-C₁₀         branched alkoxy group is substituted by —C≡C—, —CH═CH—, —CF₂O—,         —O—, —COO—, —OCO—, or —OOC—, and/or at least one hydrogen atom         of the C₁-C₁₀ linear alkyl group, the C₃-C₁₀ branched alkyl         group, the C₁-C₁₀ linear alkoxy group, or the C₃-C₁₀ branched         alkoxy group is substituted by a halogen atom;

-   -   each of X¹ and X² independently represents or     -   wherein Y¹ represents —OH, a C₁-C₁₅ alkyl group, or a C₂-C₁₅         alkenyl group, and at least one hydrogen atom of the C₁-C₁₅         alkyl group or the C₂-C₁₅ alkenyl group is substituted by —OH;     -   Y² represents hydrogen, halogen, a C₁-C₁₅ alkyl group, or a         C₂-C₁₅ alkenyl group, wherein the C₁-C₁₅ alkyl group or the         C₂-C₁₅ alkenyl group is unsubstituted or at least one hydrogen         atom of the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is         substituted by a halogen atom;     -   Z² represents a single bond, a C₁-C₁₅ alkylene group, a C₁-C₁₅         alkyleneoxy group, —C≡C—, —CH═CH—, —CF₂O—, —OCF₂—, —COO—, —OCO—,         —OOC—, —CF₂—CF₂—, or —CF═CF—;     -   A³ represents a 1,4-phenylene group, a 1,4-cyclohexylene group,         a benzofuran-2,5-diyl group, or an indane-2,5-diyl group,         wherein the 1,4-phenylene group, the 1,4-cyclohexylene group,         the benzofuran-2,5-diyl group, or the indane-2,5-diyl group is         unsubstituted or at least one hydrogen atom of the 1,4-phenylene         group, the 1,4-cyclohexylene group, the benzofuran-2,5-diyl         group, or the indane-2,5-diyl group is substituted by a halogen         atom, —CH₃, —CH₂CH₃, or a —CN group, and/or at least one —CH₂—         of the 1,4-phenylene group, the 1,4-cyclohexylene group, the         benzofuran-2,5-diyl group, or the indane-2,5-diyl group is         substituted by —O—, —N— or —S—, and wherein the —O—, —N—, and         —S— do not directly bond to one another;     -   n³+n⁴=3, n⁴ represents 2 or 3, and the two or more L² groups are         identical to each other or different from each other, and the         two or more X¹ groups are identical to each other or different         from each other;     -   n⁵+n⁶=3, n⁶ represents 2 or 3, and the two or more L² groups are         identical to each other or different from each other, and the         two or more X² groups are identical to each other or different         from each other;     -   n⁷ represents 0, 1, or 2, and when n⁷ represents 2, the two K³         groups are identical to each other or different from each other;     -   n⁸ represents 1 or 2, and when n⁸ represents 2, the two Z²         groups are identical to each other or different from each other,         the two A³ groups are identical to each other or different from         each other, and the two K³ groups are identical to each other or         different from each other;     -   when n⁸ represents 1, n⁷ represents 2;     -   when n⁸ represents 2, n⁷ in the A³ group directly bonded to the         K² group represents 2, and n⁷ in the A³ group directly bonded to         the Z² group represents 0, 1, or 2; and     -   K² represents a structure represented by formula (Id), formula         (Ie), or formula (If):

and

-   -   K³ represents a structure represented by formula (Ig) or formula         (Ih):

-   -   wherein, in formula (Id), formula (Ie), formula (If), formula         (Ig), and formula (Ih),     -   each of L¹, L², L³, L⁴, L⁵, L⁶, and L⁷ independently represents         a single bond, a C₁-C₁₅ linear alkylene group, a C₃-C₁₅ branched         alkylene group, a C₁-C₁₅ linear alkyleneoxy group, or a C₃-C₁₅         branched alkyleneoxy group, wherein the C₁-C₁₅ linear alkylene         group, the C₃-C₁₅ branched alkylene group, the C₁-C₁₅ linear         alkyleneoxy group, or the C₃-C₁₅ branched alkyleneoxy group is         unsubstituted or at least one —CH₂— of the C₁-C₁₅ linear         alkylene group, the C₃-C₁₅ branched alkylene group, the C₁-C₁₅         linear alkyleneoxy group, or the C₃-C₁₅ branched alkyleneoxy         group is substituted by —C≡C—, —CH═CH—, —CF₂O—, —SiR^(a) ₂—,         —O—, —COO—, —OCO—, or —OOC—, and/or at least one hydrogen atom         of the C₁-C₁₅ linear alkylene group, the C₃-C₁₅ branched         alkylene group, the C₁-C₁₅ linear alkyleneoxy group, or the         C₃-C₁₅ branched alkyleneoxy group is substituted by a halogen         atom, and wherein R^(a) represents a C₁-C₁₀ linear alkyl group         or a C₃-C₁₀ branched alkyl group, and two R^(a) groups bonded to         the same Si atom are identical to each other or different from         each other;     -   each of R², R³, R⁴, R⁵ and R⁶ independently represents fluorine,         chlorine, hydrogen, a C₁-C₁₀ linear alkyl group, a C₃-C₁₀         branched alkyl group, a C₁-C₁₀ linear alkoxy group, or a C₃-C₁₀         branched alkoxy group, wherein the C₁-C₁₀ linear alkyl group,         the C₃-C₁₀ branched alkyl group, the C₁-C₁₀ linear alkoxy group,         or the C₃-C₁₀ branched alkoxy group is unsubstituted or at least         one —CH₂— of the C₁-C₁₀ linear alkyl group, the C₃-C₁₀ branched         alkyl group, the C₁-C₁₀ linear alkoxy group, or the C₃-C₁₀         branched alkoxy group is substituted by —C≡C—, —CH═CH—, —CF₂O—,         —O—, —COO—, —OCO—, —OOC—, and/or at least one hydrogen atom of         the C₁-C₁₀ linear alkyl group, the C₃-C₁₀ branched alkyl group,         the C₁-C₁₀ linear alkoxy group, or the C₃-C₁₀ branched alkoxy         group is substituted by a halogen atom;     -   each of X³, X⁴, X⁵ and X⁶ independently represents hydrogen,         —OH,

and at least one of X³, X⁴, X⁵ and X⁶ represents

-   -   wherein Y¹ represents —OH, a C₁-C₁₅ alkyl group, or a C₂-C₁₅         alkenyl group, and at least one hydrogen atom of the C₁-C₁₅         alkyl group or the C₂-C₁₅ alkenyl group is substituted by —OH;     -   Y² represents hydrogen, halogen, a C₁-C₁₅ alkyl group, or a         C₂-C₁₅ alkenyl group, wherein the C₁-C₁₅ alkyl group or the         C₂-C₁₅ alkenyl group is unsubstituted or at least one hydrogen         atom of the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is         substituted by a halogen atom;     -   n⁹+n¹⁰=3, n¹⁰ represents 2 or 3, and the two or more L⁷ groups         are identical to each other or different from each other, and         the two or more X⁴ groups are identical to each other or         different from each other;     -   n¹² represents 1, 2, or 3, n¹¹+n¹²=3, and when n¹² represents 2         or 3, the two or more L² groups are identical to each other or         different from each other, and the two or more X⁵ groups are         identical to each other or different from each other; when n¹¹         represents 2, the two R² groups are identical to each other or         different from each other; and     -   n¹⁴ represents 1, 2, or 3, n¹³+n¹⁴=3, and when n¹⁴ represents 2         or 3, the two or more L² groups are identical to each other or         different from each other, and the two or more X⁶ groups are         identical to each other or different from each other; when n¹³         represents 2, the two R⁴ groups are identical to each other or         different from each other; and     -   when X⁵ or X⁶ represents,

K² represents

In other embodiments of the present disclosure, a liquid-crystal composition is provided. The liquid-crystal composition includes a first component and a second component. The first component includes at least one additive as mentioned above, and the second component includes at least one compound represented by formula (II):

wherein

each of R²¹ and R²² independently represents hydrogen, halogen, a C₁-C₁₅ alkyl group, or a C₂-C₁₅ alkenyl group, wherein the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is unsubstituted or at least one hydrogen atom of the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is substituted by a halogen atom, and/or at least one —CH₂— of the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is substituted by —O—, and wherein the —O— does not directly bond to another —O—;

each of B¹, B², and B³ independently represents a 1,4-phenylene group, a 1,4-cyclohexylene group, a benzofuran-2,5-diyl group, a 1,3-dioxane-2,5-diyl group, a tetrahydropyran-2,5-diyl group, a divalent dioxabicyclo[2.2.2]octylene group, a divalent trioxabicyclo[2.2.2]octylene group, a tetrahydronaphthalene-2,6-diyl group, or a indane-2,5-diyl group, wherein the 1,4-phenylene group, the 1,4-cyclohexylene group, the 1,3-dioxane-2,5-diyl group, the benzofuran-2,5-diyl group, the tetrahydronaphthalene-2,6-diyl group, the indane-2,5-diyl group, or the tetrahydropyran-2,5-diyl group is unsubstituted or at least one hydrogen atom of the 1,4-phenylene group, the 1,4-cyclohexylene group, the 1,3-dioxane-2,5-diyl group, the benzofuran-2,5-diyl group, the tetrahydronaphthalene-2,6-diyl group, the indane-2,5-diyl group, or the tetrahydropyran-2,5-diyl group is substituted by a halogen atom or a —CN group, and/or at least one —CH₂— of the 1,4-phenylene group, the 1,4-cyclohexylene group, the 1,3-dioxane-2,5-diyl group, the benzofuran-2,5-diyl group, the tetrahydronaphthalene-2,6-diyl group, the indane-2,5-diyl group, or the tetrahydropyran-2,5-diyl group is substituted by —O—, —N— or —S—, and wherein the —O—, —N—, and —S— do not directly bond to one another;

each of Z²¹ and Z²² independently represents a single bond, a C₁-C₄ alkylene group, a C₂-C₄ alkenylene group, or a C₂-C₄ alkynylene group, wherein the C₁-C₄ alkylene group, the C₂-C₄ alkenylene group, or the C₂-C₄ alkynylene group is unsubstituted or at least one hydrogen atom of the C₁-C₄ alkylene group, the C₂-C₄ alkenylene group, or the C₂-C₄ alkynylene group is substituted by a halogen atom or a —CN group, and/or at least one —CH₂— of the C₁-C₄ alkylene group, the C₂-C₄ alkenylene group, or the C₂-C₄ alkynylene group is substituted by —O— or —S—, and wherein the —O— does not directly bond to —O— or —S—, and —S— does not directly bond to —S—; and

n²¹ represents 0, 1, or 2, and when n²¹ represents 2, the two B¹ groups are identical to each other or different from each other.

In other embodiments of the present disclosure, a liquid-crystal display device is provided. The liquid-crystal display device includes a first substrate and a second substrate disposed opposite to the first substrate. The liquid-crystal display device also includes a liquid-crystal layer disposed between the first substrate and the second substrate. The liquid-crystal layer includes the above-mentioned additive.

Embodiments of the present disclosure provide an additive, and a liquid-crystal composition and a liquid-crystal display device using the additive, which can greatly improve the vertical alignment property, voltage holding ratio, and stability of the alignment ability of the liquid-crystal composition. Therefore, the performance and durability of the liquid-crystal display device can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

To further simplify and clarify the foregoing contents and other objects, characteristics, and merits of the present disclosure, a detailed description is given in the following embodiments with reference to the accompanying drawings. It should be emphasized that many features are not drawn to scale according to industry standard practice. In fact, the dimensions of the various components may be arbitrarily increased or decreased for clarity of discussion.

FIG. 1 is a cross-sectional view showing a liquid-crystal display device in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

In the present specification, the term “about” or “approximately” means in a range of 20% of a given value or range, preferably 10%, and more preferably 5%. In the present specification, if there is no specific explanation, a given value or range means an approximate value which may imply the meaning of “about” or “approximately”.

In the present specification, when two or more functional groups using the same code are included in one chemical formula, the two groups may be identical to each other or different from each other. For example, in formula (1), when n¹ is 2, two A¹ groups may be identical to each other or different from each other, and two Z¹ groups may also be identical to each other or different from each other. In other words, the description of “two A¹ groups and Z¹ groups are independently identical to each other or different from each other” may include all the following cases: (1) the two A¹ groups are identical to each other, and the two Z¹ groups are identical to each other; (2) the two A¹ groups are different from each other, but the two Z¹ groups are identical to each other; (3) the two A¹ groups are identical to each other, but the two Z¹ groups are different from each other; and (4) the two A¹ groups are different from each other, and the two Z¹ groups are different from each other.

In the present specification, the wavy line is used to indicate the atom to which this functional group is bonded to another functional group. For example, in the functional group,

the leftmost oxygen atom is the atom bonded to another functional group.

In some embodiments of the present disclosure, an additive is provided. The additive can greatly improve the vertical alignment degree, voltage holding ratio, and stability of the alignment ability of the liquid-crystal composition. In the present specification, the term “vertical alignment ability of the additive molecule” means the degree of vertical alignment of liquid-crystal molecules in a liquid-crystal composition when the additive is added to the liquid-crystal composition. More specifically, by adding the additive molecule to the liquid-crystal composition, most liquid-crystal molecules can be vertically aligned well without using a conventional alignment film (for example, a polyimide film). Furthermore, the liquid-crystal display device using the additive has a high voltage holding ratio and excellent performance.

In some embodiments, an additive is provided. The additive includes an additive molecule having a structure represented by formula (I):

-   -   wherein, in formula (I),     -   R¹ represents fluorine, chlorine, hydrogen, a C₁-C₂₀ linear         alkyl group, a C₃-C₂₀ branched alkyl group, a C₁-C₂₀ linear         alkoxy group, or a C₃-C₂₀ branched alkoxy group, wherein the         C₁-C₂₀ linear alkyl group, the C₃-C₂₀ branched alkyl group, the         C₁-C₂₀ linear alkoxy group, or the C₃-C₂₀ branched alkoxy group         is unsubstituted or at least one —CH₂— of the C₁-C₂₀ linear         alkyl group, the C₃-C₂₀ branched alkyl group, the C₁-C₂₀ linear         alkoxy group, or the C₃-C₂₀ branched alkoxy group is substituted         by —C≡C—, —CH═CH—, —CF₂O—, —O—, —COO—, —OCO—, or —OOC—, and/or         at least one hydrogen atom of the C₁-C₂₀ linear alkyl group, the         C₃-C₂₀ branched alkyl group, the C₁-C₂₀ linear alkoxy group, or         the C₃-C₂₀ branched alkoxy group is substituted by a halogen         atom;     -   A¹ represents a 1,4-phenylene group, a 1,4-cyclohexylene group,         a benzofuran-2,5-diyl group, a 1,3-dioxane-2,5-diyl group, a         tetrahydropyran-2,5-diyl group, a divalent         dioxabicyclo[2.2.2]octylene group, a divalent         trioxabicyclo[2.2.2]octylene group, a         tetrahydronaphthalene-2,6-diyl group, a 1,3-cyclopentylene, a         1,3-cyclobutylene, or an indane-2,5-diyl group, wherein the         1,4-phenylene group, the 1,4-cyclohexylene group, the         tetrahydronaphthalene-2,6-diyl group, the 1,3-cyclopentylene,         the 1,3-cyclobutylene, or the indane-2,5-diyl group is         unsubstituted or at least one hydrogen atom of the 1,4-phenylene         group, the 1,4-cyclohexylene group, the         tetrahydronaphthalene-2,6-diyl group, the 1,3-cyclopentylene,         the 1,3-cyclobutylene, or the indane-2,5-diyl group is         substituted by a halogen atom, —CH₃, —CH₂CH₃, or a —CN group,         and/or at least one —CH₂— of the 1,4-phenylene group, the         1,4-cyclohexylene group, the tetrahydronaphthalene-2,6-diyl         group, the 1,3-cyclopentylene, the 1,3-cyclobutylene, or the         indane-2,5-diyl group is substituted by —O—, —N— or —S—, and         wherein the —O—, —N—, and —S— do not directly bond to one         another;     -   A² represents a 1,4-phenylene group, a 1,4-cyclohexylene group,         a benzofuran-2,5-diyl group, or an indane-2,5-diyl group,         wherein the 1,4-phenylene group, the 1,4-cyclohexylene group,         the benzofuran-2,5-diyl group, or the indane-2,5-diyl group is         unsubstituted or at least one hydrogen atom of the 1,4-phenylene         group, the 1,4-cyclohexylene group, the benzofuran-2,5-diyl         group, or the indane-2,5-diyl group is substituted by a halogen         atom, —CH₃, —CH₂CH₃, or a —CN group, and/or at least one —CH₂—         of the 1,4-phenylene group, the 1,4-cyclohexylene group, the         benzofuran-2,5-diyl group, or the indane-2,5-diyl group is         substituted by —O—, —N— or —S—, and wherein the —O—, —N—, and         —S— do not directly bond to one another;     -   Z¹ represents a single bond, a C₁-C₁₅ alkylene group, a C₁-C₁₅         alkyleneoxy group, —C≡C—, —CH═CH—, —CF₂O—, —OCF₂—, —COO—, —OCO—,         —OOC—, —CF₂—CF₂—, or —CF═CF—;     -   n¹ represents 1, 2, or 3, and when n¹ represents 2 or 3, the two         or more A¹ groups are identical to each other or different from         each other, and the two or more Z¹ groups are identical to each         other or different from each other;     -   n² represents 0 or 1; and     -   K¹ represents a structure represented by formula (Ia), formula         (Ib), or formula (Ic):

-   -   wherein, in formula (Ia), formula (Ib), and formula (Ic),     -   each of L¹, L², and L³ independently represents a single bond, a         C₁-C₁₅ linear alkylene group, a C₃-C₁₅ branched alkylene group,         a C₁-C₁₅ linear alkyleneoxy group, or a C₃-C₁₅ branched         alkyleneoxy group, wherein the C₁-C₁₅ linear alkylene group, the         C₃-C₁₅ branched alkylene group, the C₁-C₁₅ linear alkyleneoxy         group, or the C₃-C₁₅ branched alkyleneoxy group is unsubstituted         or at least one —CH₂— of the C₁-C₁₅ linear alkylene group, the         C₃-C₁₅ branched alkylene group, the C₁-C₁₅ linear alkyleneoxy         group, or the C₃-C₁₅ branched alkyleneoxy group is substituted         by —C≡C—, —CH═CH—, —CF₂O—, —SiR^(a) ₂—, —O—, —COO—, —OCO—, or         —OOC—, and/or at least one hydrogen atom of the C₁-C₁₅ linear         alkylene group, the C₃-C₁₅ branched alkylene group, the C₁-C₁₅         linear alkyleneoxy group, or the C₃-C₁₅ branched alkyleneoxy         group is substituted by a halogen atom, and wherein R^(a)         represents a C₁-C₁₀ linear alkyl group or a C₃-C₁₀ branched         alkyl group, and two R^(a) groups bonded to the same Si atom are         identical to each other or different from each other;     -   each of R², R³ and R⁴ independently represents fluorine,         chlorine, hydrogen, a C₁-C₁₀ linear alkyl group, a C₃-C₁₀         branched alkyl group, a C₁-C₁₀ linear alkoxy group, or a C₃-C₁₀         branched alkoxy group, wherein the C₁-C₁₀ linear alkyl group,         the C₃-C₁₀ branched alkyl group, the C₁-C₁₀ linear alkoxy group,         or the C₃-C₁₀ branched alkoxy group is unsubstituted or at least         one —CH₂— of the C₁-C₁₀ linear alkyl group, the C₃-C₁₀ branched         alkyl group, the C₁-C₁₀ linear alkoxy group, or the C₃-C₁₀         branched alkoxy group is substituted by —C≡C—, —CH═CH—, —CF₂O—,         —O—, —COO—, —OCO—, or —OOC—, and/or at least one hydrogen atom         of the C₁-C₁₀ linear alkyl group, the C₃-C₁₀ branched alkyl         group, the C₁-C₁₀ linear alkoxy group, or the C₃-C₁₀ branched         alkoxy group is substituted by a halogen atom;     -   each of X¹ and X² independently represents

-   -   wherein Y¹ represents —OH, a C₁-C₁₅ alkyl group, or a C₂-C₁₅         alkenyl group, and at least one hydrogen atom of the C₁-C₁₅         alkyl group or the C₂-C₁₅ alkenyl group is substituted by —OH;     -   Y² represents hydrogen, halogen, a C₁-C₁₅ alkyl group, or a         C₂-C₁₅ alkenyl group, wherein the C₁-C₁₅ alkyl group or the         C₂-C₁₅ alkenyl group is unsubstituted or at least one hydrogen         atom of the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is         substituted by a halogen atom;     -   Z² represents a single bond, a C₁-C₁₅ alkylene group, a C₁-C₁₅         alkyleneoxy group, —C≡C—, —CH═CH—, —CF₂O—, —OCF₂—, —COO—, —OCO—,         —OOC—, —CF₂—CF₂—, or —CF═CF—;     -   A³ represents a 1,4-phenylene group, a 1,4-cyclohexylene group,         a benzofuran-2,5-diyl group, or an indane-2,5-diyl group,         wherein the 1,4-phenylene group, the 1,4-cyclohexylene group,         the benzofuran-2,5-diyl group, or the indane-2,5-diyl group is         unsubstituted or at least one hydrogen atom of the 1,4-phenylene         group, the 1,4-cyclohexylene group, the benzofuran-2,5-diyl         group, or the indane-2,5-diyl group is substituted by a halogen         atom, —CH₃, —CH₂CH₃, or a —CN group, and/or at least one —CH₂—         of the 1,4-phenylene group, the 1,4-cyclohexylene group, the         benzofuran-2,5-diyl group, or the indane-2,5-diyl group is         substituted by —O—, —N— or —S—, and wherein the —O—, —N—, and         —S— do not directly bond to one another;     -   n³+n⁴=3, n⁴ represents 2 or 3, and the two or more L² groups are         identical to each other or different from each other, and the         two or more X¹ groups are identical to each other or different         from each other;     -   n⁵+n⁶=3, n⁶ represents 2 or 3, and the two or more L² groups are         identical to each other or different from each other, and the         two or more X² groups are identical to each other or different         from each other;     -   n⁷ represents 0, 1, or 2, and when n⁷ represents 2, the two K³         groups are identical to each other or different from each other;     -   n⁸ represents 1 or 2, and when n⁸ represents 2, the two Z²         groups are identical to each other or different from each other,         the two A³ groups are identical to each other or different from         each other, and the two K³ groups are identical to each other or         different from each other;     -   when n⁸ represents 1, n⁷ represents 2;     -   when n⁸ represents 2, n⁷ in the A³ group directly bonded to the         K² group represents 2, and n⁷ in the A³ group directly bonded to         the Z² group represents 0, 1, or 2; and     -   K² represents a structure represented by formula (Id), formula         (Ie), or formula (If):

and

-   -   K³ represents a structure represented by formula (Ig) or formula         (Ih):

-   -   wherein, in formula (Id), formula (Ie), formula (If), formula         (Ig), and formula (Ih),     -   each of L¹, L², L³, L⁴, L⁵, L⁶, and L⁷ independently represents         a single bond, a C₁-C₁₅ linear alkylene group, a C₃-C₁₅ branched         alkylene group, a C₁-C₁₅ linear alkyleneoxy group, or a C₃-C₁₅         branched alkyleneoxy group, wherein the C₁-C₁₅ linear alkylene         group, the C₃-C₁₅ branched alkylene group, the C₁-C₁₅ linear         alkyleneoxy group, or the C₃-C₁₅ branched alkyleneoxy group is         unsubstituted or at least one —CH₂— of the C₁-C₁₅ linear         alkylene group, the C₃-C₁₅ branched alkylene group, the C₁-C₁₅         linear alkyleneoxy group, or the C₃-C₁₅ branched alkyleneoxy         group is substituted by —C≡C—, —CH═CH—, —CF₂O—, —SiR^(a) ₂—,         —O—, —COO—, —OCO—, or —OOC—, and/or at least one hydrogen atom         of the C₁-C₁₅ linear alkylene group, the C₃-C₁₅ branched         alkylene group, the C₁-C₁₅ linear alkyleneoxy group, or the         C₃-C₁₅ branched alkyleneoxy group is substituted by a halogen         atom, and wherein R^(a) represents a C₁-C₁₀ linear alkyl group         or a C₃-C₁₀ branched alkyl group, and two R^(a) groups bonded to         the same Si atom are identical to each other or different from         each other;     -   each of R², R³, R⁴, R⁵ and R⁶ independently represents fluorine,         chlorine, hydrogen, a C₁-C₁₀ linear alkyl group, a C₃-C₁₀         branched alkyl group, a C₁-C₁₀ linear alkoxy group, or a C₃-C₁₀         branched alkoxy group, wherein the C₁-C₁₀ linear alkyl group,         the C₃-C₁₀ branched alkyl group, the C₁-C₁₀ linear alkoxy group,         or the C₃-C₁₀ branched alkoxy group is unsubstituted or at least         one —CH₂— of the C₁-C₁₀ linear alkyl group, the C₃-C₁₀ branched         alkyl group, the C₁-C₁₀ linear alkoxy group, or the C₃-C₁₀         branched alkoxy group is substituted by —C≡C—, —CH═CH—, —CF₂O—,         —O—, —COO—, —OCO—, or —OOC—, and/or at least one hydrogen atom         of the C₁-C₁₀ linear alkyl group, the C₃-C₁₀ branched alkyl         group, the C₁-C₁₀ linear alkoxy group, or the C₃-C₁₀ branched         alkoxy group is substituted by a halogen atom;     -   each of X³, X⁴, X⁵ and X⁶ independently represents hydrogen,         —OH,

and at least one of X³, X⁴, X⁵ and X⁶ represents

-   -   wherein Y¹ represents —OH, a C₁-C₁₅ alkyl group, or a C₂-C₁₅         alkenyl group, and at least one hydrogen atom of the C₁-C₁₅         alkyl group or the C₂-C₁₅ alkenyl group is substituted by —OH;     -   Y² represents hydrogen, halogen, a C₁-C₁₅ alkyl group, or a         C₂-C₁₅ alkenyl group, wherein the C₁-C₁₅ alkyl group or the         C₂-C₁₅ alkenyl group is unsubstituted or at least one hydrogen         atom of the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is         substituted by a halogen atom;     -   n⁹+n¹⁰=3, n¹⁰ represents 2 or 3, and the two or more L⁷ groups         are identical to each other or different from each other, and         the two or more X⁴ groups are identical to each other or         different from each other;     -   n¹² represents 1, 2, or 3, n¹¹+n¹²=3, and when n¹² represents 2         or 3, the two or more L² groups are identical to each other or         different from each other, and the two or more X⁵ groups are         identical to each other or different from each other; when n¹¹         represents 2, the two R² groups are identical to each other or         different from each other; and     -   n¹⁴ represents 1, 2, or 3, n¹³+n¹⁴=3, and when n¹⁴ represents 2         or 3, the two or more L² groups are identical to each other or         different from each other, and the two or more X⁶ groups are         identical to each other or different from each other; when n¹³         represents 2, the two R⁴ groups are identical to each other or         different from each other; and     -   when X⁵ or X⁶ represents

K² represents -L⁴-R⁵.

In other embodiments, the additive includes an additive molecule having a structure represented by formula (I):

-   -   wherein, in formula (I),     -   R¹ represents fluorine, chlorine, hydrogen, a C₁-C₁₅ linear         alkyl group, a C₃-C₁₅ branched alkyl group, a C₁-C₁₅ linear         alkoxy group, or a C₃-C₁₅ branched alkoxy group, wherein the         C₁-C₁₅ linear alkyl group, the C₃-C₁₅ branched alkyl group, the         C₁-C₁₅ linear alkoxy group, or the C₃-C₁₅ branched alkoxy group         is unsubstituted or at least one —CH₂— of the C₁-C₁₅ linear         alkyl group, the C₃-C₁₅ branched alkyl group, the C₁-C₁₅ linear         alkoxy group, or the C₃-C₁₅ branched alkoxy group is substituted         by —CH═CH—, —CF₂O—, —O—, —COO—, —OCO—, or —OOC—, and/or at least         one hydrogen atom of the C₁-C₁₅ linear alkyl group, the C₃-C₁₅         branched alkyl group, the C₁-C₁₅ linear alkoxy group, or the         C₃-C₁₅ branched alkoxy group is substituted by a halogen atom;     -   the definitions of A¹, A², Z¹, n¹, and n² are respectively the         same as the definitions of A, A², Z¹, n¹, and n² defined in the         previous paragraphs; and     -   K¹ represents a structure represented by formula (I′a), formula         (I′b), or formula (I′c):

-   -   wherein, in formula (I′a), formula (I′b), and formula (I′c),     -   the definitions of L², L³, n³, n⁴, n⁵, and n⁶ are respectively         the same as the definitions of L², L³, n³, n⁴, n⁵, and n⁶         defined in the previous paragraphs;     -   each of R², R³ and R⁴ independently represents fluorine,         chlorine, hydrogen, a C₁-C₈ linear alkyl group, a C₃-C₈ branched         alkyl group, a C₁-C₈ linear alkoxy group, or a C₃-C₈ branched         alkoxy group, wherein the C₁-C₈ linear alkyl group, the C₃-C₈         branched alkyl group, the C₁-C₈ linear alkoxy group, or the         C₃-C₈ branched alkoxy group is unsubstituted or at least one         —CH₂— of the C₁-C₈ linear alkyl group, the C₃-C₈ branched alkyl         group, the C₁-C₈ linear alkoxy group, or the C₃-C₈ branched         alkoxy group is substituted by —CH═CH—, —CF₂O—, —O—, —COO—,         —OCO—, or —OOC—, and/or at least one hydrogen atom of the C₁-C₈         linear alkyl group, the C₃-C₈ branched alkyl group, the C₁-C₈         linear alkoxy group, or the C₃-C₈ branched alkoxy group is         substituted by a halogen atom;

-   -   each of X¹ and X² independently represents or;     -   wherein Y¹ represents —OH, a C₁-C₈ alkyl group, or a C₂-C₈         alkenyl group, and at least one hydrogen atom of the C₁-C₈ alkyl         group or the C₂-C₈ alkenyl group is substituted by —OH;     -   Y² represents hydrogen, halogen, a C₁-C₈ alkyl group, or a C₂-C₈         alkenyl group, wherein the C₁-C₈ alkyl group or the C₂-C₈         alkenyl group is unsubstituted or at least one hydrogen atom of         the C₁-C₈ alkyl group or the C₂-C₈ alkenyl group is substituted         by a halogen atom;     -   K² represents a structure represented by formula (Id), formula         (Ie), or formula (If):

and

-   -   K³ represents a structure represented by formula (Ig) or formula         (Ih):

-   -   wherein, in formula (Id), formula (Ie), formula (If), formula         (Ig), and formula (Ih),     -   the definitions of L¹, L², L³, L⁴, L⁵, L⁶, L⁷, n⁹, n¹⁰, n¹¹,         n¹², n¹³, and n¹⁴ are respectively the same as the definitions         of L¹, L², L³, L⁴, L⁵, L⁶, L⁷, n⁹, n¹⁰, n¹¹, n¹², n¹³, and n¹⁴         defined in the previous paragraphs;     -   each of R², R³, R⁴, R⁵ and R⁶ independently represents fluorine,         chlorine, hydrogen, a C₁-C₈ linear alkyl group, a C₃-C₈ branched         alkyl group, a C₁-C₈ linear alkoxy group, or a C₃-C₈ branched         alkoxy group, wherein the C₁-C₈ linear alkyl group, the C₃-C₈         branched alkyl group, the C₁-C₈ linear alkoxy group, or the         C₃-C₈ branched alkoxy group is unsubstituted or at least one         —CH₂— of the C₁-C₈ linear alkyl group, the C₃-C₈ branched alkyl         group, the C₁-C₈ linear alkoxy group, or the C₃-C₈ branched         alkoxy group is substituted by —CH═CH—, —CF₂O—, —O—, —COO—,         —OCO—, or —OOC—, and/or at least one hydrogen atom of the C₁-C₈         linear alkyl group, the C₃-C₈ branched alkyl group, the C₁-C₈         linear alkoxy group, or the C₃-C₈ branched alkoxy group is         substituted by a halogen atom;     -   each of X³, X⁴, X⁵ and X⁶ independently represents hydrogen,         —OH,

-   -   wherein Y¹ represents —OH, a C₁-C₈ alkyl group, or a C₂-C₈         alkenyl group, and at least one hydrogen atom of the C₁-C₈ alkyl         group or the C₂-C₈ alkenyl group is substituted by —OH;     -   Y² represents hydrogen, halogen, a C₁-C₈ alkyl group, or a C₂-C₈         alkenyl group, wherein the C₁-C₈ alkyl group or the C₂-C₈         alkenyl group is unsubstituted or at least one hydrogen atom of         the C₁-C₈ alkyl group or the C₂-C₈ alkenyl group is substituted         by a halogen atom;     -   wherein at least one of X³, X⁴, X⁵ and X⁶ represents

and

-   -   when X⁵ or X⁶ represents

K² represents -L⁴-R⁵.

The structure represented by formula (I) is substantially a rod-shaped structure. This rod-shaped structure has a first axial direction and a second axial direction. The first axial direction is the long axial direction of the rod-shaped structure, that is, the direction in which the functional group R¹ and the functional group K¹ are connected. The second axial direction is the short axial direction of the rod-shaped structure, that is, a direction perpendicular to the first axial direction.

In formula (I), at least one of the functional groups X¹, X², X³, X⁴, X⁵, and X⁶ may include an anchoring group. As a result, the additive molecules can be fixed to the substrate (for example, the first substrate 110 or the second substrate 120 shown in FIG. 1). The anchoring group may be a functional group having a higher polarity. The anchoring group may generate a bond or a hydrogen bond with a substrate (for example, glass or ITO), and therefore, the additive molecules can be adsorbed (or fixed) on the substrate. For example, the anchoring group may include —OH,

In order to achieve a state in which the liquid-crystal molecules are well aligned vertically, the additive molecules may be fixed on the substrate in such a manner that the first axial direction is perpendicular to the top surface of the substrate. In some embodiments, the anchoring group is one of X¹, X², X³, X⁴, X⁵, and X⁶ that is closest to the right end of the molecule represented by formula (I) such that the first axis is perpendicular to the top surface of the substrate.

In some embodiments, each of the additive molecules has only one anchoring group. Therefore, each of the additive molecules has the same alignment direction on the substrate. In other words, the first axial directions of the different additive molecules are parallel to each other. As a result, the liquid-crystal molecules can be aligned in a uniform state, and defects (for example, local bright spots generated in the dark state) are not easy to generate. In other embodiments, each of the additive molecules has two anchoring groups. Therefore, it is helpful for the immobilization of the additive molecules on the substrate without being easy to detach. As a result, the occurrence of defects can also be reduced. In addition, in order to avoid the polarity of the additive molecules being too high to be dissolved in the liquid-crystal composition, the number of anchoring groups in one additive molecule is at most three.

In the above formula (I), the cyclic functional groups (i.e., A¹ and A²) may be an aliphatic ring or an aromatic ring. The cyclic functional group contributes to the alignment of the liquid-crystal molecules. More specifically, the aromatic cyclic functional group may generate a π-π stacking so that the rod-shaped liquid-crystal molecules may be aligned in a specific direction. The aliphatic cyclic functional group can align the rod-shaped liquid-crystal molecules in a specific direction by steric hindrance. In some embodiments, the first axial direction of the additive molecules is perpendicular to the top surface of the substrate, and the long axis of the rod-shaped liquid-crystal molecules is parallel to the first axial direction of the additive molecules. Therefore, the long axis of the rod-shaped liquid-crystal molecules can be made perpendicular to the substrate by the additive molecules. In other words, the vertical alignment of the liquid-crystal molecules can be achieved.

Some negative ions (for example, fluoride ions) may remain in the liquid-crystal composition. These ions can cause residual current and reduce the voltage holding ratio during the operation of the display. More specifically, the higher concentration of the negative ions results in the lower the voltage holding ratio. Silicon atoms are more electron-poor than carbon atoms, and therefore, silicon atoms can attract (or capture) the negative ions in the liquid-crystal composition. As a result, the concentration of the negative ions in the liquid-crystal composition can be lowered, and the voltage holding ratio of the liquid-crystal display device can be increased. In other words, in the molecule represented by formula (I), the silicon atom has the function of increasing the voltage holding ratio. Furthermore, in order to attract the negative ions, the silicon atom in the molecule represented by formula (I) is not directly bonded to the oxygen atom. In addition, because the silicon atom is bonded to the alkyl group, the solubility of the molecule represented by formula (I) in the liquid-crystal composition can also be improved.

In some embodiments, in the above formula (I), at least one of the functional groups X¹, X², X³, X⁴, X⁵, and X⁶ may include a polymerizable group. The polymerizable group may undergo the polymerization reaction with another polymerizable group by irradiation or heating, and the two polymerizable groups may be bonded to each other. When a plurality of additive molecules are fixed on the substrate, the polymerizable group of the additive molecule undergoes the polymerization reaction with the polymerizable group of the adjacent additive molecule. In this way, a plurality of the additive molecules that are perpendicular to the substrate and arranged in parallel with each other can form a network structure. This network structure can avoid the tilt of the additive molecules. As a result, the degree of vertical alignment of the liquid-crystal molecules is further improved, and the stability of the alignment ability is improved. The polymerizable group may include an acrylic group, a methacrylic group, or a derivative thereof. In some embodiments, at least one of the functional groups X¹, X², X³, X⁴, X⁵, and X⁶ is a polymerizable group having the following structure or

and wherein Y¹ represents —OH, a C₁-C₈ alkyl group, or a C₂-C₈ alkenyl group, and at least one hydrogen atom of the C₁-C₈ alkyl group or the C₂-C₈ alkenyl group is substituted by —OH; and Y² represents hydrogen, halogen, a C₁-C₈ alkyl group, or a C₂-C₈ alkenyl group, wherein the C₁-C₈ alkyl group or the C₂-C₈ alkenyl group is unsubstituted or at least one hydrogen atom of the C₁-C₈ alkyl group or the C₂-C₈ alkenyl group is substituted by a halogen atom.

In other embodiments, the additive includes the first additive molecule, and the first additive molecule has a structure represented by formula (I):

-   -   wherein, in formula (I),     -   R¹ represents fluorine, chlorine, hydrogen, a C₁-C₁₅ linear         alkyl group, a C₃-C₁₅ branched alkyl group, a C₁-C₁₅ linear         alkoxy group, or a C₃-C₁₅ branched alkoxy group, wherein the         C₁-C₁₅ linear alkyl group, the C₃-C₁₅ branched alkyl group, the         C₁-C₁₅ linear alkoxy group, or the C₃-C₁₅ branched alkoxy group         is unsubstituted or at least one —CH₂— of the C₁-C₁₅ linear         alkyl group, the C₃-C₁₅ branched alkyl group, the C₁-C₁₅ linear         alkoxy group, or the C₃-C₁₅ branched alkoxy group is substituted         by —CH═CH—, —CF₂O—, —O—, —COO—, —OCO—, or —OOC—, and/or at least         one hydrogen atom of the C₁-C₁₅ linear alkyl group, the C₃-C₁₅         branched alkyl group, the C₁-C₁₅ linear alkoxy group, or the         C₃-C₁₅ branched alkoxy group is substituted by a halogen atom;     -   the definitions of A¹, A², Z¹, n¹, and n² are respectively the         same as the definitions of A, A², Z¹, n¹, and n² defined in the         previous paragraphs; and     -   K¹ represents a structure represented by formula (I′a), formula         (I′b), or formula (I′c):

-   -   wherein, in formula (I′a), formula (I′b), and formula (I′c),     -   the definitions of L², L³, n³, n⁴, n⁵, and n⁶ are respectively         the same as the definitions of L², L³, n³, n⁴, n⁵, and n⁶         defined in the previous paragraphs;     -   each of R², R³, and R⁴ independently represents fluorine,         chlorine, hydrogen, a C₁-C₈ linear alkyl group, a C₃-C₈ branched         alkyl group, a C₁-C₈ linear alkoxy group, or a C₃-C₈ branched         alkoxy group, wherein the C₁-C₈ linear alkyl group, the C₃-C₈         branched alkyl group, the C₁-C₈ linear alkoxy group, or the         C₃-C₈ branched alkoxy group is unsubstituted or at least one         —CH₂— of the C₁-C₈ linear alkyl group, the C₃-C₈ branched alkyl         group, the C₁-C₈ linear alkoxy group, or the C₃-C₈ branched         alkoxy group is substituted by —CH═CH—, —CF₂O—, —O—, —COO—,         —OCO—, or —OOC—, and/or at least one hydrogen atom of the C₁-C₈         linear alkyl group, the C₃-C₈ branched alkyl group, the C₁-C₈         linear alkoxy group, or the C₃-C₈ branched alkoxy group is         substituted by a halogen atom;     -   each of X¹ and X² independently represents

-   -   wherein Y¹ represents —OH, a C₁-C₈ alkyl group, or a C₂-C₈         alkenyl group, and at least one hydrogen atom of the C₁-C₈ alkyl         group or the C₂-C₈ alkenyl group is substituted by —OH;     -   Y² represents hydrogen, halogen, a C₁-C₈ alkyl group, or a C₂-C₈         alkenyl group, wherein the C₁-C₈ alkyl group or the C₂-C₈         alkenyl group is unsubstituted or at least one hydrogen atom of         the C₁-C₈ alkyl group or the C₂-C₈ alkenyl group is substituted         by a halogen atom;     -   K² represents a structure represented by formula (Id), formula         (Ie), or formula (If):

and

-   -   K³ represents a structure represented by formula (Ig) or formula         (Ih):

-   -   wherein, in formula (Id), formula (Ie), formula (If), formula         (Ig), and formula (Ih),     -   the definitions of L¹, L², L³, L⁴, L⁵, L⁶, L, n⁹, n¹⁰, n¹¹, n¹²,         n¹³, and n¹⁴ are respectively the same as the definitions of L¹,         L², L³, L⁴, L⁵, L⁶, L⁷, n⁹, n¹⁰, n¹¹, n¹², n¹³, and n¹⁴ defined         in the previous paragraphs;     -   each of R², R³, R⁴, R⁵ and R⁶ independently represents fluorine,         chlorine, hydrogen, a C₁-C₈ linear alkyl group, a C₃-C₈ branched         alkyl group, a C₁-C₈ linear alkoxy group, or a C₃-C₈ branched         alkoxy group, wherein the C₁-C₈ linear alkyl group, the C₃-C₈         branched alkyl group, the C₁-C₈ linear alkoxy group, or the         C₃-C₈ branched alkoxy group is unsubstituted or at least one         —CH₂— of the C₁-C₈ linear alkyl group, the C₃-C₈ branched alkyl         group, the C₁-C₈ linear alkoxy group, or the C₃-C₈ branched         alkoxy group is substituted by —CH═CH—, —CF₂O—, —O—, —COO—,         —OCO—, or —OOC—, and/or at least one hydrogen atom of the C₁-C₅         linear alkyl group, the C₃-C₈ branched alkyl group, the C₁-C₈         linear alkoxy group, or the C₃-C₈ branched alkoxy group is         substituted by a halogen atom;     -   each of X³, X⁴, X⁵ and X⁶ independently represents hydrogen,         —OH,

and the definitions of Y¹ and Y² are respectively the same as the definitions of Y¹ and Y² defined in this paragraph;

-   -   when K¹ represents the structure represented by formula (I′a) or         formula (I′b), at least one of X¹ and X² represents

-   -   when K¹ represents the structure represented by formula (I′c),         and K² represents the structure represented by formula (Id), at         least one of X⁵ and X⁶ represents

-   -   when K¹ represents the structure represented by formula (I′c),         and K² represents the structure represented by formula (Ie) or         formula (If), at least one of X³, X⁴, X⁵ and X⁶ represents

In other embodiments, the additive includes the second additive molecule, and the second additive molecule has a structure represented by formula (I):

-   -   wherein, in formula (I),     -   R¹ represents fluorine, chlorine, hydrogen, a C₁-C₁₅ linear         alkyl group, a C₃-C₁₅ branched alkyl group, a C₁-C₁₅ linear         alkoxy group, or a C₃-C₁₅ branched alkoxy group, wherein the         C₁-C₁₅ linear alkyl group, the C₃-C₁₅ branched alkyl group, the         C₁-C₁₅ linear alkoxy group, or the C₃-C₁₅ branched alkoxy group         is unsubstituted or at least one —CH₂— of the C₁-C₁₅ linear         alkyl group, the C₃-C₁₅ branched alkyl group, the C₁-C₁₅ linear         alkoxy group, or the C₃-C₁₅ branched alkoxy group is substituted         by —CH═CH—, —CF₂O—, —O—, —COO—, —OCO—, or —OOC—, and/or at least         one hydrogen atom of the C₁-C₁₅ linear alkyl group, the C₃-C₁₅         branched alkyl group, the C₁-C₁₅ linear alkoxy group, or the         C₃-C₁₅ branched alkoxy group is substituted by a halogen atom;     -   the definitions of A¹, A², Z¹, n¹, and n² are respectively the         same as the definitions of A, A², Z¹, n¹, and n² defined in the         previous paragraphs; and     -   K¹ represents a structure represented by formula (I′a), formula         (I′b), or formula (I′c):

-   -   wherein, in formula (I′a), formula (I′b), and formula (I′c),     -   the definitions of L², L³, n³, n⁴, n⁵, and n⁶ are respectively         the same as the definitions of L², L³, n³, n⁴, n⁵, and n⁶         defined in the previous paragraphs;     -   each of R², R³, and R⁴ independently represents fluorine,         chlorine, hydrogen, a C₁-C₈ linear alkyl group, a C₃-C₈ branched         alkyl group, a C₁-C₈ linear alkoxy group, or a C₃-C₈ branched         alkoxy group, wherein the C₁-C₈ linear alkyl group, the C₃-C₈         branched alkyl group, the C₁-C₈ linear alkoxy group, or the         C₃-C₈ branched alkoxy group is unsubstituted or at least one         —CH₂— of the C₁-C₈ linear alkyl group, the C₃-C₈ branched alkyl         group, the C₁-C₈ linear alkoxy group, or the C₃-C₈ branched         alkoxy group is substituted by —CH═CH—, —CF₂O—, —O—, —COO—,         —OCO—, or —OOC—, and/or at least one hydrogen atom of the C₁-C₈         linear alkyl group, the C₃-C₈ branched alkyl group, the C₁-C₈         linear alkoxy group, or the C₃-C₈ branched alkoxy group is         substituted by a halogen atom;     -   each of X¹ and X² independently represents

-   -   wherein Y¹ represents —OH, a C₁-C₈ alkyl group, or a C₂-C₈         alkenyl group, and at least one hydrogen atom of the C₁-C₈ alkyl         group or the C₂-C₈ alkenyl group is substituted by —OH;     -   Y² represents hydrogen, halogen, a C₁-C₈ alkyl group, or a C₂-C₈         alkenyl group, wherein the C₁-C₈ alkyl group or the C₂-C₈         alkenyl group is unsubstituted or at least one hydrogen atom of         the C₁-C₈ alkyl group or the C₂-C₈ alkenyl group is substituted         by a halogen atom;     -   K² represents a structure represented by formula (Id), formula         (Ie), or formula (If):

and

-   -   K³ represents a structure represented by formula (Ig) or formula         (Ih):

-   -   wherein, in formula (Id), formula (Ie), formula (If), formula         (Ig), and formula (Ih),     -   the definitions of L¹, L², L³, L⁴, L⁵, L⁶, L⁷, n⁹, n¹⁰, n¹¹,         n¹², n¹³, and n¹⁴ are respectively the same as the definitions         of L¹, L², L³, L⁴, L⁵, L⁶, L⁷, n⁹, n¹⁰, n¹¹, n¹², n¹³ and n¹⁴         defined in the previous paragraphs;     -   each of R², R³, R⁴, R⁵ and R⁶ independently represents fluorine,         chlorine, hydrogen, a C₁-C₈ linear alkyl group, a C₃-C₈ branched         alkyl group, a C₁-C₈ linear alkoxy group, or a C₃-C₈ branched         alkoxy group, wherein the C₁-C₈ linear alkyl group, the C₃-C₅         branched alkyl group, the C₁-C₈ linear alkoxy group, or the         C₃-C₈ branched alkoxy group is unsubstituted or at least one         —CH₂— of the C₁-C₈ linear alkyl group, the C₃-C₈ branched alkyl         group, the C₁-C₈ linear alkoxy group, or the C₃-C₈ branched         alkoxy group is substituted by —CH═CH—, —CF₂O—, —O—, —COO—,         —OCO—, or —OOC—, and/or at least one hydrogen atom of the C₁-C₅         linear alkyl group, the C₃-C₈ branched alkyl group, the C₁-C₈         linear alkoxy group, or the C₃-C₈ branched alkoxy group is         substituted by a halogen atom;     -   each of X³, X⁴, X⁵ and X⁶ independently represents hydrogen,         —OH,

and the definitions of Y¹ and Y² are respectively the same as the definitions of Y¹ and Y² defined in this paragraph;

-   -   when K¹ represents the structure represented by formula (I′a) or         formula (I′b), each of X¹ and X² independently represents

-   -   when K¹ represents the structure represented by formula (I′c),         each of X³, X⁴, X⁵ and X⁶ independently represents hydrogen or

Specific exemplary first additive molecules are shown in Table 1 below. Specific exemplary second additive molecules are shown in Table 2 below.

TABLE 1

Exp-A1

Exp-A2

Exp-A3

Exp-A4

Exp-A5

Exp-A6

Exp-A7

Exp-A8

TABLE 2

Exp-B1

Exp-B2

Exp-B3

Exp-B4

Exp-B5

Exp-B6

Referring to Table 1, in the first additive molecule, the functional group at the end of the molecular main chain includes a polymerizable group and an anchoring group. Therefore, the first additive molecule can be adsorbed (or fixed) on the substrate in such a manner that the first axial direction is perpendicular to the top surface of the substrate, thereby obtaining good vertical alignment ability. Furthermore, a plurality of first additive molecules that are perpendicular to the substrate and arranged in parallel with each other can form the above-mentioned network structure. This network structure can further improve the degree of vertical alignment of the liquid-crystal molecules and improve the stability of the alignment ability.

Referring to Table 2, in the second additive molecule, the molecular side chain includes at least one polymerizable group. The second additive molecule may form the above-mentioned network structure with the adjacent second additive molecule or the first additive molecule. As a result, the stability of the alignment ability can be improved.

In some embodiments, the additive includes a first additive molecule. Therefore, this additive can have excellent vertical alignment ability and good stability of the alignment ability. In other embodiments, the additive includes a second additive molecule. In still other embodiments, the additive includes a first additive molecule and a second additive molecule. In such embodiments, the first additive molecules may be vertically fixed on the substrate, and the first additive molecules may be bonded to adjacent first additive molecules or second additive molecules to form the above-mentioned network structure. Therefore, this additive can have excellent vertical alignment ability and excellent stability of the alignment ability. In some embodiments, the additive includes a first additive molecule and a second additive molecule, and when the amount of the first additive molecule is set to 1 part by weight, the amount of the second additive molecule is 0.1-60 parts by weight. In other embodiments, when the amount of the first additive molecule is set to 1 part by weight, the amount of the second additive molecule is 0.5-50 parts by weight. In still other embodiments, when the amount of the first additive molecule is set to 1 part by weight, the amount of the second additive molecule is 1-30 parts by weight.

In other embodiments, a liquid-crystal composition is provided. The liquid-crystal composition includes a first component and a second component. The first component includes at least one additive as mentioned above, and the second component includes at least one compound represented by formula (II):

-   -   wherein     -   each of R²¹ and R²² independently represents hydrogen, halogen,         a C₁-C₁₅ alkyl group, or a C₂-C₁₅ alkenyl group, wherein the         C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is unsubstituted         or at least one hydrogen atom of the C₁-C₁₅ alkyl group or the         C₂-C₁₅ alkenyl group is substituted by a halogen atom, and/or at         least one —CH₂— of the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl         group is substituted by —O—, and wherein the —O— does not         directly bond to another —O—;     -   each of B¹, B², and B³ independently represents a 1,4-phenylene         group, a 1,4-cyclohexylene group, a benzofuran-2,5-diyl group, a         1,3-dioxane-2,5-diyl group, a tetrahydropyran-2,5-diyl group, a         divalent dioxabicyclo[2.2.2]octylene group, a divalent         trioxabicyclo[2.2.2]octylene group, a         tetrahydronaphthalene-2,6-diyl group, or an indane-2,5-diyl         group, wherein the 1,4-phenylene group, the 1,4-cyclohexylene         group, the 1,3-dioxane-2,5-diyl group, the benzofuran-2,5-diyl         group, the tetrahydronaphthalene-2,6-diyl group, the         indane-2,5-diyl group, or the tetrahydropyran-2,5-diyl group is         unsubstituted or at least one hydrogen atom of the 1,4-phenylene         group, the 1,4-cyclohexylene group, the 1,3-dioxane-2,5-diyl         group, the benzofuran-2,5-diyl group, the         tetrahydronaphthalene-2,6-diyl group, the indane-2,5-diyl group,         or the tetrahydropyran-2,5-diyl group is substituted by a         halogen atom or a —CN group, and/or at least one —CH₂— of the         1,4-phenylene group, the 1,4-cyclohexylene group, the         1,3-dioxane-2,5-diyl group, the benzofuran-2,5-diyl group, the         tetrahydronaphthalene-2,6-diyl group, the indane-2,5-diyl group,         or the tetrahydropyran-2,5-diyl group is substituted by —O—, —N—         or —S—, and wherein the —O—, —N—, and —S— do not directly bond         to one another;     -   each of Z²¹ and Z²² independently represents a single bond, a         C₁-C₄ alkylene group, a C₂-C₄ alkenylene group, or a C₂-C₄         alkynylene group, wherein the C₁-C₄ alkylene group, the C₂-C₄         alkenylene group, or the C₂-C₄ alkynylene group is unsubstituted         or at least one hydrogen atom of the C₁-C₄ alkylene group, the         C₂-C₄ alkenylene group, or the C₂-C₄ alkynylene group is         substituted by a halogen atom or a —CN group, and/or at least         one —CH₂— of the C₁-C₄ alkylene group, the C₂-C₄ alkenylene         group, or the C₂-C₄ alkynylene group is substituted by —O— or         —S—, and wherein the —O— does not directly bond to —O— or —S—,         and —S— does not directly bond to —S—; and     -   n²¹ represents 0, 1, or 2, and when n²¹ represents 2, the two B¹         groups are identical to each other or different from each other.

In accordance with some embodiments, the above-mentioned second component includes at least one compound represented by formula (II-1) or formula (II-2):

-   -   wherein     -   the definitions of R²¹, R²², B¹, B², Z²², and n²¹ are         respectively the same as the definitions of R²¹, R²², B¹, B²,         Z²², and n²¹ defined in the previous paragraphs.

Because the cyclic group of the compound of formula (II-1) has no fluorine atom, the viscosity of the liquid-crystal composition can be lowered, and the response speed of the liquid-crystal molecules can be improved when a voltage is applied. The compound of formula (II-2) includes at least one phenylene group, and two hydrogen atoms on the same side of this phenylene group are substituted by fluorine atoms. The compound of formula (II-2) can be used to adjust the dielectric anisotropy (Δε) of the liquid-crystal composition.

In accordance with some embodiments, the above-mentioned liquid-crystal composition further includes a third component, and the third component includes at least one compound represented by formula (III), formula (IV), or formula (V):

-   -   wherein     -   each of K²¹, K²², K²³, and K²⁴ independently represents hydrogen         or a methyl group;     -   each of Z²³ and Z²⁴ independently represents a single bond, a         C₁-C₁₅ linear alkylene group, a C₃-C₁₅ branched alkylene group,         a C₂-C₁₅ linear alkenylene group, or a C₃-C₁₅ branched         alkenylene group, wherein the C₁-C₁₅ linear alkylene group, the         C₃-C₁₅ branched alkylene group, the C₂-C₁₅ linear alkenylene         group, or the C₃-C₁₅ branched alkenylene group is unsubstituted         or at least one hydrogen atom of the C₁-C₁₅ linear alkylene         group, the C₃-C₁₅ branched alkylene group, the C₂-C₁₅ linear         alkenylene group, or the C₃-C₁₅ branched alkenylene group is         substituted by a halogen atom, and/or at least one —CH₂— of the         C₁-C₁₅ linear alkylene group, the C₃-C₁₅ branched alkylene         group, the C₂-C₁₅ linear alkenylene group, or the C₃-C₁₅         branched alkenylene group is substituted by —O—, —CO—, —COO—, or         —OCO—, and wherein the —O—, —CO—, —COO—, and —OCO— do not         directly bond to one another;     -   each of Z²⁵, Z²⁶, Z²⁷, and Z²⁸ independently represents a single         bond, —C≡C—, a C₁-C₁₅ linear alkylene group, a C₃-C₁₅ branched         alkylene group, a C₂-C₁₅ linear alkenylene group, or a C₃-C₁₅         branched alkenylene group, wherein the C₁-C₁₅ linear alkylene         group, the C₃-C₁₅ branched alkylene group, the C₂-C₁₅ linear         alkenylene group, or the C₃-C₁₅ branched alkenylene group is         unsubstituted or at least one hydrogen atom of the C₁-C₁₅ linear         alkylene group, the C₃-C₁₅ branched alkylene group, the C₂-C₁₅         linear alkenylene group, or the C₃-C₁₅ branched alkenylene group         is substituted by a halogen atom, and/or at least one —CH₂— of         the C₁-C₁₅ linear alkylene group, the C₃-C₁₅ branched alkylene         group, the C₂-C₁₅ linear alkenylene group, or the C₃-C₁₅         branched alkenylene group is substituted by —SiR^(e) ₂—, —S—,         —O—, —CO—, —COO—, —OCO—, —CO—NR^(e)—, or —NR^(e)—CO—, and the         —SiR^(e) ₂—, —S—, —O—, —CO—, —COO—, —OCO—, —CO—NR^(e)—, and         —NR^(e)—CO— do not directly bond to one another, wherein R^(e)         represents hydrogen, a C₁-C₄ linear alkyl group, or a C₃-C₄         branched alkyl group, and the two R^(e) groups bonded to the         same Si atom are identical to each other or different from each         other;     -   each of B⁴, B⁵, B⁶ and B⁷ independently represents a         1,4-phenylene group, a 1,4-cyclohexylene group, a         benzofuran-2,5-diyl group, a 1,3-dioxane-2,5-diyl group, a         tetrahydropyran-2,5-diyl group, a divalent         dioxabicyclo[2.2.2]octylene group, a divalent         trioxabicyclo[2.2.2]octylene group, a         tetrahydronaphthalene-2,6-diyl group, or an indane-2,5-diyl         group, wherein the 1,4-phenylene group, the 1,4-cyclohexylene         group, the benzofuran-2,5-diyl group, the 1,3-dioxane-2,5-diyl         group, the tetrahydropyran-2,5-diyl group, the divalent         dioxabicyclo[2.2.2]octylene group, the divalent         trioxabicyclo[2.2.2]octylene group, the         tetrahydronaphthalene-2,6-diyl group, or the indane-2,5-diyl         group is unsubstituted or is substituted by at least one         substituent, wherein the at least one substituent is selected         from fluorine, chlorine, a —CN group, a C₁-C₁₂ linear alkyl         group, a C₃-C₁₂ branched alkyl group, a C₂-C₁₂ linear alkenyl         group, a C₂-C₁₂ linear alkynyl group, a C₄-C₁₂ branched alkenyl         group, or a C₄-C₁₂ branched alkynyl group, wherein the C₁-C₁₂         linear alkyl group, the C₃-C₁₂ branched alkyl group, the C₂-C₁₂         linear alkenyl group, the C₂-C₁₂ linear alkynyl group, the         C₄-C₁₂ branched alkenyl group, or the C₄-C₁₂ branched alkynyl         group is unsubstituted or at least one hydrogen atom of the         C₁-C₁₂ linear alkyl group, the C₃-C₁₂ branched alkyl group, the         C₂-C₁₂ linear alkenyl group, the C₂-C₁₂ linear alkynyl group,         the C₄-C₁₂ branched alkenyl group, or the C₄-C₁₂ branched         alkynyl group is substituted by a halogen atom, and/or at least         one —CH₂— of the C₁-C₁₂ linear alkyl group, the C₃-C₁₂ branched         alkyl group, the C₂-C₁₂ linear alkenyl group, the C₂-C₁₂ linear         alkynyl group, the C₄-C₁₂ branched alkenyl group, or the C₄-C₁₂         branched alkynyl group is substituted by —O—, —CO—, —COO—, or         —OCO—, and the —O—, —CO—, —COO—, and —OCO— do not directly bond         to one another;     -   M¹ represents a single bond, —CH₂O—, —OCH₂—, —CH₂CH₂—, —CH═CH—,         —C ≡C—, —CH₂—, —C(CH₃)₂—, —C(CF₃)₂—, —SiH₂—, —Si(CH₃)₂—, or         —Si(CF₃)₂—;     -   each of R²³ and R²⁴ independently represents a C₁-C₃₀ linear         alkyl group or a C₃-C₃₀ branched alkyl group, wherein the C₁-C₃₀         linear alkyl group or the C₃-C₃₀ branched alkyl group is         unsubstituted or at least one hydrogen atom of the C₁-C₃₀ linear         alkyl group or the C₃-C₃₀ branched alkyl group is substituted by         a halogen atom, and/or at least one —CH₂— of the C₁-C₃₀ linear         alkyl group or the C₃-C₃₀ branched alkyl group is substituted by         —Si—, —O—, —CO—, —COO—, or —OCO—, and the —Si—, —O—, —CO—,         —COO—, and —OCO— do not directly bond to one another; and     -   each of n²² and n²³ independently represents an integer of 0 to         3, and when n²² is 2 or more, the two or more B⁴ groups are         identical to each other or different from each other, and the         two or more M¹ groups are identical to each other or different         from each other; and when n²³ is 2 or more, the two or more B⁶         groups are identical to each other or different from each other,         and the two or more Z²⁷ groups are identical to each other or         different from each other.

The compound of the third component includes at least one polymerizable group, and the polymerizable group may include an acrylic group, a methacrylic group, or a derivative thereof. More specifically, each of the compounds represented by formula (IV) and formula (V) has a polymerizable group at one end of the molecule. Each of the compounds represented by formula (III) has a polymerizable group at both ends of the molecule. By irradiation or heating, the polymerizable group of the third component may undergo the polymerization reaction with another polymerizable group of the above-mentioned additive molecules represented by formula (I). In this way, it is helpful to form the above-mentioned network, and the degree of vertical alignment of the liquid-crystal molecules can be further improved.

If the content of the first component is too low, the degree of vertical alignment and the voltage holding ratio of the liquid-crystal composition may not be effectively improved. On the contrary, if the content of the first component is too high, the first component may not dissolve well in the liquid-crystal composition, and it may precipitate. Such a liquid-crystal composition cannot be used. Furthermore, when the first component exceeds the specific content, even if the first component is further increased, the degree of vertical alignment of the liquid-crystal composition cannot be further improved. Furthermore, the first component has the group (for example, an anchoring group) having a relatively high polarity. Therefore, if the content of the first component is too high, the voltage holding ratio of the liquid-crystal composition may be lowered. As described above, in order to balance the degree of vertical alignment and the voltage holding ratio of the liquid-crystal composition, the content of the first component may be controlled within an appropriate range.

In some embodiments, the liquid-crystal composition includes a first component and a second component. In such embodiments, when the total weight of the second component is 100 parts by weight, the first component is 0.01-10 parts by weight. In other embodiments, when the total weight of the second component is 100 parts by weight, the first component is 0.05-5 parts by weight. In still other embodiments, when the total weight of the second component is 100 parts by weight, the first component is 0.1-3 parts by weight.

In some embodiments, the liquid-crystal composition includes a first component, a second component, and a third component. In such embodiments, when the total weight of the second component is 100 parts by weight, the first component is 0.01-10 parts by weight, and the third component is 0.01-10 parts by weight. In other embodiments, when the total weight of the second component is 100 parts by weight, the first component is 0.04-3.5 parts by weight, and the third component is 0.04-3.5 parts by weight. In still other embodiments, when the total weight of the second component is 100 parts by weight, the first component is 0.07-2 parts by weight, and the third component is 0.07-2 parts by weight.

For those skilled in the art, it should be understood that the liquid-crystal composition may further include other components other than the above-mentioned first component, second component, and third component. For example, other conventional liquid-crystal compounds or other additives in appropriate amounts. In some embodiments, the above-mentioned other additives may include, for example, chiral dopants, UV stabilizers, antioxidants, free radical scavengers, nanoparticles, and so on.

In the present disclosure, a liquid-crystal display device using the above-mentioned liquid-crystal composition is also provided. FIG. 1 is a cross-sectional view showing a liquid-crystal display device 100 in accordance with some embodiments of the present disclosure.

Referring to FIG. 1, the liquid-crystal display device 100 includes a first substrate 110 and a second substrate 120 disposed opposite to the first substrate 110. The liquid-crystal display device 100 also includes a liquid-crystal layer 130 disposed between the first substrate 110 and the second substrate 120. The first substrate 110 and the second substrate 120 are respectively a conventional thin film transistor substrate and a conventional color filter substrate. In order to simplify the description, the materials, structures, and manufacturing methods of the first substrate 110 and the second substrate 120 will not be described in detail herein.

The liquid-crystal layer 130 of the liquid-crystal display device 100 of the present disclosure uses the above-mentioned liquid-crystal composition, and the liquid-crystal composition includes the additive represented by formula (I). As described above, the additive represented by the formula (I) can greatly improve the degree of vertical alignment, the voltage holding ratio, and the stability of the alignment ability of the liquid-crystal composition. By adding the additive represented by formula (I) to the liquid-crystal composition, the liquid-crystal molecules can be vertically aligned well without using a conventional alignment film. On the other hand, the liquid-crystal display device 100 using the additive of the present disclosure has the advantages of high voltage holding ratio and good durability. The liquid-crystal composition of the present disclosure can be applied to all kinds of liquid-crystal display devices.

In order to further simplify and clarify the foregoing contents and other objects, characteristics, and merits of the present disclosure, a few examples are given to explain the additives and the liquid-crystal compositions of the present disclosure. The chemical structures and contents corresponding to the compounds of the second component and the third component used in the liquid-crystal compositions of the Examples are shown in Table 3 below. The additive molecules of the Examples and the Reference Examples are shown in Table 1, Table 2 (shown above), and Table 4 below.

TABLE 3 Content Chemical structure (wt %) formula (II) formula (II-1)

10

5

12

14 formula (II-2)

10

19

15

15 formula (III)

0.3

TABLE 4 No. Classification Chemical structure Exp-C formula (V)

Ref —

The synthesis methods of the additive molecules of the Examples and the Reference Examples are described as follows.

Preparation Example 1 Preparing the Additive Molecule Exp-A1

Compound 1 (35 g, 89.5 mmol) and anhydrous tetrahydrofuran (550 mL) were placed in a 1000 mL reaction flask and stirred to dissolve. Then, n-butyllithium (2.5 M, solvent: tetrahydrofuran; 39.4 mL, 98.5 mmol) was slowly added to the reaction flask at −78° C., and the reaction was carried out for 1 hour. Next, dimethylchlorosilane (10.16 g, 107.4 mmol) was added to the reaction flask at −78° C., and the reaction was carried out at room temperature (20-30° C.) for 2 hours. After the reaction was completed, dilute hydrochloric acid (1 N, 30 mL) was added. Then, an extraction was performed by using ethyl acetate and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain Compound 2.

Compound 2 (8.0 g, 21.6 mmol), toluene (60 mL) and platinum-containing catalyst (Pt/C, Pt content: 5 wt %, 0.84 g) were placed in a 250 mL double-necked flask, and nitrogen gas was introduced. Then, diethyl diallylmalonate (5.2 g, 25.6 mmol) was added and heated to 80° C. for 8 hours to carry out the reaction. After the reaction was completed, the platinum-containing catalyst was removed by filtration. Then, an extraction was performed by using toluene and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain Compound 3.

Lithium aluminum hydride (LAH, 2.66 g, 70.1 mmol) and anhydrous tetrahydrofuran (160 mL) were placed in a 500 mL reaction flask and stirred to dissolve. Then, Compound 3 (20.0 g, 35.0 mmol) was slowly added to the reaction flask at 0° C., and the reaction was carried out for 1 hour. Next, the reaction was carried out at room temperature (20-30° C.) for 6 hours. After the reaction was completed, water was added. Then, an extraction was performed by using ethyl acetate and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain Compound 4.

Compound 4 (2.0 g, 4.1 mmol), methacrylic acid (0.35 g, 4.1 mmol), 4-dimethylaminopyridine (DMAP, 0.25 g, 2.0 mmol), and dichloromethane (100 mL) were placed in a 250 mL reaction flask and stirred to dissolve. Then, N,N′-dicyclohexylcarbodiimide (DCC, 1.0 g, 4.9 mmol) was added to the reaction flask at 0° C., and the reaction was carried out at room temperature (20-30° C.) for 8 hours. After the reaction was completed, water was added. Then, an extraction was performed by using dichloromethane and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain Compound 5.

Compound 5 (1.2 g, 2.2 mmol), acrylic acid (0.62 g, 8.7 mmol), 4-dimethylaminopyridine (0.13 g, 1.1 mmol), and dichloromethane (60 mL) were placed in a 250 mL reaction flask and stirred to dissolve. Then, N,N′-dicyclohexylcarbodiimide (0.54 g, 2.6 mmol) was added to the reaction flask at 0° C., and the reaction was carried out at room temperature (20-30° C.) for 8 hours. After the reaction was completed, water was added. Then, an extraction was performed by using dichloromethane and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain Compound 6.

Compound 6 (0.6 g, 1.0 mmol), paraformaldehyde (0.24 g, 7.9 mmol), 1,4-diazabicyclo[2.2.2]octane (0.42 g, 3.7 mmol), water (7 mL), and tetrahydrofuran (20 mL) were placed in a 100 mL reaction flask and stirred to dissolve. Then, the reaction was carried out at 70° C. for 8 hours. After the reaction was completed, water was added. Then, an extraction was performed by using ethyl acetate and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain the additive molecule Exp-A1.

The additive molecule Exp-A1 was analyzed by nuclear magnetic resonance spectroscopy, and the obtained spectral information was as follows: ¹H NMR (CDCl₃, 400 MHz): δ 0.23 (s, 6H), 0.73-0.74 (m, 2H), 0.86-1.43 (m, 25H), 1.72-1.92 (m, 12H), 2.05-2.15 (m, 1H), 2.30-2.50 (m, 2H), 4.09-4.17 (m, 4H), 4.31 (d, J=5.6 Hz, 2H), 5.56 (s, 1H), 5.83 (s, 1H), 6.08 (s, 1H), 6.23 (s, 1H), 7.19 (d, J=8.0 Hz, 2H), 7.40 (d, J=8.0 Hz, 2H).

Preparation Example 2 Preparing the Additive Molecule Exp-B2

Compound 4 (5.0 g, 10.3 mmol), acrylic acid (4.1 g, 56.5 mmol), 4-dimethylaminopyridine (1.25 g, 10.3 mmol), and dichloromethane (200 mL) were placed in a 500 mL reaction flask and stirred to dissolve. Then, N,N′-dicyclohexylcarbodiimide (5.1 g, 24.7 mmol) was added to the reaction flask at 0° C., and the reaction was carried out at room temperature (20-30° C.) for 24 hours. After the reaction was completed, water was added. Then, an extraction was performed by using dichloromethane and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain the additive molecule Exp-B2.

The additive molecule Exp-B2 was analyzed by nuclear magnetic resonance spectroscopy, and the obtained spectral information was as follows: ¹H NMR (CDCl₃, 400 MHz): δ 0.23 (s, 6H), 0.72-0.74 (m, 2H), 0.86-1.44 (m, 26H), 1.72-1.90 (m, 8H), 2.02-2.15 (m, 1H), 2.35-2.45 (m, 1H), 4.08-4.18 (m, 4H), 5.82 (dd, J₁=10.4 Hz, J₂=1.6 Hz, 2H), 6.10 (dd, J₁=17.2 Hz, J₂=10.4 Hz, 2H), 6.38 (dd, J=17.2 Hz, J₂=1.6 Hz, 2H), 7.19 (d, J=8.0 Hz, 2H), 7.40 (d, J=8.0 Hz, 2H).

Preparation Example 3 Preparing the Additive Molecule Exp-A2

The additive molecule Exp-B2 (1.5 g, 2.5 mmol), paraformaldehyde (0.68 g, 22.7 mmol), 1,4-diazabicyclo[2.2.2]octane (1.1 g, 10.0 mmol), water (15 mL), and tetrahydrofuran (30 mL) were placed in a 100 mL reaction flask and stirred to dissolve. Then, the reaction was carried out at 70° C. for 8 hours. After the reaction was completed, water was added. Then, an extraction was performed by using ethyl acetate and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain the additive molecule Exp-A2.

The additive molecule Exp-A2 was analyzed by nuclear magnetic resonance spectroscopy, and the obtained spectral information was as follows: ¹H NMR (CDCl₃, 400 MHz): δ 0.24 (s, 6H), 0.72-1.43 (m, 30H), 1.72-1.92 (m, 8H), 2.05-2.17 (m, 1H), 2.21-2.32 (m, 2H), 2.36-2.48 (m, 1H), 4.10-4.22 (m, 4H), 4.31 (d, J=5.6 Hz, 2H), 5.84 (s, 2H), 6.23 (s, 2H), 7.19 (d, J=8.0 Hz, 2H), 7.40 (d, J=8.0 Hz, 2H).

Preparation Example 4 Preparing the Additive Molecule Exp-B1

Compound 4 (3.0 g, 6.2 mmol), methacrylic acid (2.1 g, 24.7 mmol), 4-dimethylaminopyridine (0.75 g, 6.2 mmol), and dichloromethane (60 mL) were placed in a 250 mL reaction flask and stirred to dissolve. Then, N,N′-dicyclohexylcarbodiimide (3.0 g, 14.7 mmol) was added to the reaction flask at 0° C., and the reaction was carried out at room temperature (20-30° C.) for 24 hours. After the reaction was completed, water was added. Then, an extraction was performed by using dichloromethane and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain the additive molecule Exp-B1.

The additive molecule Exp-B1 was analyzed by nuclear magnetic resonance spectroscopy, and the obtained spectral information was as follows: ¹H NMR (CDCl₃, 400 MHz): δ 0.24 (s, 6H), 0.73-0.77 (m, 2H), 0.89-1.46 (m, 26H), 1.77-1.95 (m, 14H), 2.11-2.14 (m, 1H), 2.41-2.45 (m, 1H), 4.09-4.19 (m, 4H), 5.57 (s, 2H), 6.10 (s, 2H), 7.19 (d, J=8.0 Hz, 2H), 7.40 (d, J=8.0 Hz, 2H).

Preparation Example 5 Preparing the Additive Molecule Exp-A3

Compound 1 (24.7 g, 63.2 mmol) and anhydrous tetrahydrofuran (400 mL) were placed in a 1000 mL reaction flask and stirred to dissolve. Then, n-butyllithium (2.5 M, solvent: tetrahydrofuran; 26.5 mL, 66.2 mmol) was slowly added to the reaction flask at −78° C., and the reaction was carried out for 1 hour. Next, trichloro(methyl)silane (9.0 g, 60.2 mmol) was added to the reaction flask at −78° C., and the reaction was carried out at room temperature (20-30° C.) for 3 hours. Then, allylmagnesium chloride (concentration: 2.0M, solvent: tetrahydrofuran; 63.2 mL, 126.4 mmol) was added, and the mixture was heated (100° C.) to reflux for 8 hours to carry out the reaction. After the reaction was completed, water was added. Then, an extraction was performed by using ethyl acetate and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain Compound 7.

Compound 7 (17.0 g, 38.9 mmol) and tetrahydrofuran (550 mL) were placed in a 1000 mL reaction flask and stirred to dissolve. Then, borane-dimethyl sulfide complex (concentration: 2.0M, solvent: tetrahydrofuran; 42.8 mL, 85.6 mmol) was added to the reaction flask at 0° C., and the reaction was carried out for 3 hours. Then, sodium hydroxide (4.2 g, 105.1 mmol) was dissolved in 34 mL of pure water at 0° C. and stirred for 0.5 hour. Then, hydrogen peroxide (30%, 55 mL) was added to the reaction flask at 0° C., and the reaction was carried out at room temperature (20-30° C.) for 5 hours. After the reaction was completed, saturated potassium carbonate aqueous solution was added. Then, an extraction was performed by using ethyl acetate and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain Compound 8.

Compound 8 (6.0 g, 12.7 mmol), acrylic acid (4.6 g, 63.5 mmol), 4-dimethylaminopyridine (1.5 g, 12.7 mmol), and tetrahydrofuran (120 mL) were placed in a 500 mL reaction flask and stirred to dissolve. Then, N,N′-dicyclohexylcarbodiimide (6.3 g, 30.5 mmol) was added to the reaction flask at 0° C., and the reaction was carried out at room temperature (20-30° C.) for 24 hours. After the reaction was completed, water was added. Then, an extraction was performed by using ethyl acetate and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain Compound 9.

Compound 9 (3.0 g, 5.2 mmol), paraformaldehyde (1.4 g, 46.5 mmol), 1,4-diazabicyclo[2.2.2]octane (2.3 g, 20.7 mmol), water (22 mL), and tetrahydrofuran (45 mL) were placed in a 250 mL reaction flask and stirred to dissolve. Then, the reaction was carried out at 70° C. for 24 hours. After the reaction was completed, water was added. Then, an extraction was performed by using ethyl acetate and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain the additive molecule Exp-A3.

The additive molecule Exp-A3 was analyzed by nuclear magnetic resonance spectroscopy, and the obtained spectral information was as follows: ¹H NMR (CDCl₃, 400 MHz): δ 0.29 (s, 3H), 0.80-1.46 (m, 26H), 1.68-1.92 (m, 12H), 2.33-2.36 (m, 2H), 2.42-2.45 (m, 1H), 4.15 (t, J=6.8 Hz, 4H), 4.34 (d, J=6.4 Hz, 4H), 5.84 (s, 2H), 6.26 (s, 2H), 7.20 (d, J=8.0 Hz, 2H), 7.40 (d, J=8.0 Hz, 2H).

Preparation Example 6 Preparing the Additive Molecule Exp-B3

Compound 8 (3.0 g, 6.3 mmol), methacrylic acid (2.2 g, 25.4 mmol), 4-dimethylaminopyridine (0.77 g, 6.3 mmol), and tetrahydrofuran (100 mL) were placed in a 250 mL reaction flask and stirred to dissolve. Then, N,N′-dicyclohexylcarbodiimide (3.1 g, 15.2 mmol) was added to the reaction flask at 0° C., and the reaction was carried out at room temperature (20-30° C.) for 24 hours. After the reaction was completed, water was added. Then, an extraction was performed by using ethyl acetate and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain the additive molecule Exp-B3.

The additive molecule Exp-B3 was analyzed by nuclear magnetic resonance spectroscopy, and the obtained spectral information was as follows: ¹H NMR (CDCl₃, 400 MHz): δ 0.29 (s, 3H), 0.80-1.46 (m, 26H), 1.66-1.96 (m, 18H), 2.42-2.46 (m, 1H), 4.10 (t, J=6.8 Hz, 4H), 5.56 (s, 2H), 6.10 (s, 2H), 7.20 (d, J=8.0 Hz, 2H), 7.40 (d, J=8.0 Hz, 2H).

Preparation Example 7 Preparing the Additive Molecule Exp-A4

Compound 1 (24.2 g, 61.8 mmol) and anhydrous tetrahydrofuran (400 mL) were placed in a 1000 mL reaction flask and stirred to dissolve. Then, n-butyllithium (2.5 M, solvent: tetrahydrofuran; 25.9 mL, 64.7 mmol) was slowly added to the reaction flask at −78° C., and the reaction was carried out for 1 hour. Next, tetrachlorosilane (10.0 g, 58.9 mmol) was added to the reaction flask at −78° C., and the reaction was carried out at room temperature (20-30° C.) for 3 hours. Then, allylmagnesium chloride (concentration: 2.0M, solvent: tetrahydrofuran; 100.0 mL, 200.0 mmol) was added, and the mixture was heated (100° C.) to reflux for 8 hours to carry out the reaction. After the reaction was completed, water was added. Then, an extraction was performed by using ethyl acetate and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain Compound 10.

Compound 10 (14.0 g, 30.3 mmol) and tetrahydrofuran (470 mL) were placed in a 1000 mL reaction flask and stirred to dissolve. Then, borane-dimethyl sulfide complex (concentration: 2.0M, solvent: tetrahydrofuran; 53.0 mL, 106.0 mmol) was added to the reaction flask at 0° C., and the reaction was carried out for 3 hours. Then, sodium hydroxide (4.8 g, 121.2 mmol) was dissolved in 42 mL of pure water at 0° C. and stirred for 0.5 hour. Then, hydrogen peroxide (30%, 80 mL) was added to the reaction flask at 0° C., and the reaction was carried out at room temperature (20-30° C.) for 5 hours. After the reaction was completed, saturated potassium carbonate aqueous solution was added. Then, an extraction was performed by using ethyl acetate and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, the purificatoin was performed by recrystallization (ethyl acetate/n-hexane) to obtain Compound 11.

Compound 11 (8.0 g, 15.5 mmol), acrylic acid (11.2 g, 155.0 mmol), 4-dimethylaminopyridine (2.8 g, 23.3 mmol), and tetrahydrofuran (190 mL) were placed in a 500 mL reaction flask and stirred to dissolve. Then, N,N′-dicyclohexylcarbodiimide (11.5 g, 55.8 mmol) was added to the reaction flask at 0° C., and the reaction was carried out at room temperature (20-30° C.) for 24 hours. After the reaction was completed, water was added. Then, an extraction was performed by using ethyl acetate and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain Compound 12.

Compound 12 (2.2 g, 3.2 mmol), paraformaldehyde (0.9 g, 30.0 mmol), 1,4-diazabicyclo[2.2.2]octane (1.5 g, 13.0 mmol), water (15 mL), and tetrahydrofuran (40 mL) were placed in a 250 mL reaction flask and stirred to dissolve. Then, the reaction was carried out at 70° C. for 48 hours. After the reaction was completed, water was added. Then, an extraction was performed by using ethyl acetate and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain the additive molecule Exp-A4.

The additive molecule Exp-A4 was analyzed by nuclear magnetic resonance spectroscopy, and the obtained spectral information was as follows: ¹H NMR (CDCl₃, 400 MHz): δ 0.81-1.46 (m, 28H), 1.68-1.95 (m, 14H), 2.44-2.47 (m, 4H), 4.16 (t, J=6.8 Hz, 6H), 4.34 (d, J=6.0 Hz, 6H), 5.85 (s, 3H), 6.26 (s, 3H), 7.21 (d, J=8.0 Hz, 2H), 7.39 (d, J=8.0 Hz, 2H).

Preparation Example 8 Preparing the Additive Molecule Exp-B4

Compound 13 (30 g, 91.3 mmol), diisopropylamine (1.3 g, 12.8 mmol), N-bromosuccinimide (NBS, 33.3 g, 187.2 mmol), and dichloromethane (400 mL) were placed in a 1000 mL reaction flask and stirred to dissolve. The reaction was carried out at room temperature (20-30° C.) for 6 hours. After the reaction was completed, water was added. Then, an extraction was performed by using dichloromethane and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain Compound 14.

Sodium hydride (NaH, 4.2 g, 173 mmol), dimethylformamide (DMF, 200 mL), and Compound 14 (24.0 g, 49.4 mmol) were placed in a 500 mL double-necked flask and stirred for 30 minutes. Then, iodoethane (23.1 g, 148.1 mmol) was added at 0° C., and the reaction was carried out at 100° C. for 8 hours. After the reaction was completed, water was added. Then, an extraction was performed by using ethyl acetate and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain Compound 15.

Compound 15 (8.0 g, 15.6 mmol) and anhydrous tetrahydrofuran (100 mL) were placed in a 500 mL reaction flask and stirred to dissolve. Then, n-butyllithium (2.5 M, solvent: tetrahydrofuran; 22.4 mL, 56.0 mmol) was slowly added to the reaction flask at −78° C., and the reaction was carried out for 1 hour. Next, dimethylchlorosilane (5.3 g, 56.0 mmol) was added to the reaction flask at −78° C., and the reaction was carried out at room temperature (20-30° C.) for 2 hours. After the reaction was completed, dilute hydrochloric acid (1 N, 60 mL) was added. Then, an extraction was performed by using ethyl acetate and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain Compound 16.

Compound 16 (1.0 g, 2.1 mmol), toluene (15 mL) and platinum-containing catalyst (Pt/C, Pt content: 5 wt %, 0.2 g) were placed in a 100 mL double-necked flask, and nitrogen gas was introduced. Then, allyl methacrylate (1.1 g, 8.5 mmol) was added and heated to 100° C. for 8 hours to carry out the reaction. After the reaction was completed, the platinum-containing catalyst was removed by filtration. Then, an extraction was performed by using toluene and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain the additive molecule Exp-B4.

The additive molecule Exp-B4 was analyzed by nuclear magnetic resonance spectroscopy, and the obtained spectral information was as follows: ¹H NMR (CDCl₃, 400 MHz): δ 0.32 (s, 12H), 0.83-1.45 (m, 29H), 1.65-1.96 (m, 18H), 2.39-2.45 (m, 1H), 3.78 (q, J=7.2 Hz, 2H), 4.12 (t, J=6.8 Hz, 4H), 5.55 (s, 2H), 6.11 (s, 2H), 7.26 (s, 2H).

Preparation Example 9 Preparing the Additive Molecule Exp-C

Compound 2 (6.0 g, 16.2 mmol), toluene (50 mL) and platinum-containing catalyst (Pt/C, Pt content: 5 wt %, 0.63 g) were placed in a 250 mL double-necked flask, and nitrogen gas was introduced. Then, allyl methacrylate (3.1 g, 24.3 mmol) was added and heated to 90° C. for 8 hours to carry out the reaction. After the reaction was completed, the platinum-containing catalyst was removed by filtration. Then, an extraction was performed by using toluene and water, and the organic phase was collected. The solvent of the collected organic phase was removed by using a rotary concentrator. Then, column chromatography was performed to obtain the additive molecule Exp-C.

The additive molecule Exp-C was analyzed by nuclear magnetic resonance spectroscopy, and the obtained spectral information was as follows: ¹H NMR (CDCl₃, 400 MHz): δ 0.24 (s, 6H), 0.74-0.78 (m, 2H), 0.89-1.50 (m, 24H), 1.68-1.95 (m, 11H), 2.42-2.49 (m, 1H), 4.11 (t, J=8.0 Hz, 2H), 5.57 (s, 1H), 6.10 (s, 1H), 7.19 (d, J=8.0 Hz, 2H), 7.40 (d, J=8.0 Hz, 2H).

Preparation Example 10 Preparing the Additive Molecule Ref

The additive molecule Ref can be synthesized in accordance with the procedure for synthesizing Compound 15 by using Compound 13 as starting material, and the synthesis step is as shown in the above flow chart.

In the following Examples and Reference Examples, all of the liquid-crystal compositions were prepared by forming the mother liquid formed by 100 parts by weight of the molecules of formula (II) in accordance with Table 3, and then, 0.3 parts by weight of molecule of formula (III) shown in Table 3 was added. Next, the additive molecules shown in Tables 1, 2, and 4 were additionally added to the above liquid-crystal composition in accordance with the amount that was added, shown in Table 5. For example, the liquid-crystal composition of Example 6 is 100 parts by weight of the mother liquid formed by the molecules of formula (II) shown in Table 3, and 0.3 parts by weight of the molecule of formula (III), 0.2 parts by weight of the additive molecule Exp-A2, and 0.5 parts by weight of the additive molecule Exp-B2 is further added. Furthermore, in the liquid-crystal compositions of Reference Example and Examples 1-5 shown in Table 5, only one kind of the additive molecules shown in Tables 1, 2, and 4 was added.

Production of the Liquid-Crystal Display Device

In 100 parts by weight of the mother liquid formed by the molecules of formula (II), 0.3 parts by weight of the molecule of formula (III) shown in Table 3 and the additive molecules shown in Tables 1, 2, and 4 (the amounts that were added are shown in Table 5) were added, and the mixture was uniformly mixed and heated to the clearing point. Then, it was cooled to room temperature to form a liquid-crystal composition of a Reference Example or an Example. The liquid-crystal composition of the Example or the Reference Example is injected between two indium tin oxide (ITO) substrates having an interval of 3.5 μm and having no alignment layer to form the liquid-crystal display element of the Example or the Reference Example, respectively. A DC voltage of 12 V and irradiation of ultraviolet light (peak wavelength: 313 nm) were applied to the liquid-crystal display element to form the liquid-crystal display device of the Example or the Reference Example.

Properties of the Liquid-Crystal Composition

[Vertical Alignment]

The liquid-crystal display device was disposed in a polarizing microscope in which a polarizing element and an analyzer were arranged orthogonally. The element was irradiated with light from below, and the presence or absence of light leakage was observed to judge the vertical alignment. The experimental results of vertical alignment were shown in Table 6.

◯: Light does not pass through any part of the element (the whole piece is uniform and has no light transmission). This result indicates that the device has vertical alignment.

X: Light passes through all parts of the element (the whole piece is uniformly transmitted by light). This result indicates that the device has no vertical alignment.

[Voltage Holding Ratio]

A DC voltage (charge voltage of 5 V, operating frequency of 0.6 Hz) was applied to the liquid-crystal display of the Example or the Reference Example at an ambient temperature of 60° C. The voltage value V2 after the application was released to 1.667 sec was measured by the liquid-crystal physical parameter measuring instrument (product number: ALCT-IV1, manufactured by INSTEC Co., Ltd.). The experimental results of voltage holding ratio were shown in Table 6. The formula for calculating the voltage holding ratio (VHR) of the liquid-crystal display device is as follows:

VHR═(V2/applied voltage value)×100%.

[Stability of the Alignment Ability]

A voltage of 0V to 10V was continuously applied to the liquid-crystal display device, and the light transmittance of the liquid-crystal display device corresponding to different voltages was measured. The light transmittance was recorded every 0.1V, and a graph of voltage versus transmittance was drawn based on the experimental results. The voltage corresponding to a liquid-crystal display device having a transmittance of 1% is defined as V(th,i). Next, a deterioration experiment was performed on the liquid-crystal display device. The steps of the deterioration experiment are as follows. The liquid-crystal display device was placed in an oven (temperature: 60° C.), and a voltage (AC, 10 V) was applied for a duration of 4 days. After the deterioration experiment was performed, the liquid-crystal display device was subjected to the experiment described above, and a graph of voltage versus transmittance was drawn. The voltage corresponding to a liquid-crystal display device having a transmittance of 1% is defined as V(th,f). The AVth value (unit: Volts) of the liquid-crystal display device is calculated according to the following formula. The smaller the absolute value of AVth, the better the stability of the alignment ability of the additive molecules. The experimental results of the AVth value were shown in Table 6.

ΔVth=V(th,f)−V(th,i)

TABLE 5 Amount added Amount added Additive (parts by Additive (parts by No. molecule weight) molecule weight) Reference Ref 1.5 — — Example Example 1 Exp-A1 2.0 — — Example 2 Exp-A2 0.3 — — Example 3 Exp-A3 0.1 — — Example 4 Exp-A3 0.2 — — Example 5 Exp-B4 3.0 — — Example 6 Exp-A2 0.2 Exp-B1 0.5 Example 7 Exp-A2 0.2 Exp-B2 0.5 Example 8 Exp-A3 0.2 Exp-B3 0.5 Example 9 Exp-A3 0.2 Exp-B4 0.5 Example 10 Exp-A2 0.2 Exp-C 0.5 Example 11 Exp-A2 0.1 Exp-C 1.7 Example 12 Exp-A3 0.2 Exp-C 0.5

TABLE 6 Vertical alignment VHR (%) ΔVth value (V) Reference ◯ 37.2 −0.490 Example Example 1 ◯ 94.5 −0.419 Example 2 ◯ 96.3 −0.195 Example 3 ◯ 95.7 −0.005 Example 4 ◯ 97.5 −0.088 Example 5 ◯ 90.9 −0.040 Example 6 ◯ 89.2 −0.171 Example 7 ◯ 83.6 −0.240 Example 8 ◯ 97.5 −0.327 Example 9 ◯ 98.4 −0.022 Example 10 ◯ 98.0 −0.010 Example 11 ◯ 96.9 −0.050 Example 12 ◯ 96.2 −0.153

Referring to the Reference Example of Table 6, the Reference Example includes the additive molecule Ref Because the additive molecule Ref does not have the silicon atom and the polymerizable group, the voltage holding ratio of the liquid-crystal composition of the Reference Example is not good. Furthermore, because the additive molecule Ref does not have the polymerizable group, the stability of the vertical alignment ability of the liquid-crystal composition of the Reference Example is not good.

Referring to Examples 1-12 of Table 6, each of Examples 1-12 includes at least one additive molecule represented by formula (I). The results show that the liquid-crystal molecules of Examples 1-12 are all vertically aligned, and the voltage holding ratio (for example, the voltage holding ratio greater than 80%) and the stability of the vertical alignment ability are significantly improved.

Referring to Examples 1-4 of Table 6, each of Examples 1-4 includes one of the first additive molecules, and all of the first additive molecules include both the anchoring group and the polymerizable group. The results show that the liquid-crystal molecules of Examples 1-4 are all vertically aligned. In particular, in Examples 2, 3, and 4, the liquid-crystal molecules can be vertically aligned well in the condition that only a small amount of the additive molecules (for example, the amount that was added is less than 0.5 parts by weight) is added. Accordingly, the first additive molecule can significantly improve the degree of vertical alignment of the liquid-crystal molecules, and can also significantly improve the voltage holding ratio.

Referring to Example 5 of Table 6, Example 5 includes one of the second additive molecules, and the second additive molecule includes two polymerizable groups at the side chain and/or main chain of the molecule. The results show that the liquid-crystal molecules of Example 5 are vertically aligned, and the stability of their alignment ability is excellent. Accordingly, the second additive molecule can significantly improve the degree of stability of the vertical alignment ability of the liquid-crystal molecules.

Referring to Examples 6-9 of Table 6, each of Examples 6-9 includes one of the first additive molecules and one of the second additive molecules, and all of the second additive molecules include two polymerizable groups at the side chain and/or main chain of the molecule. The results show that the liquid-crystal molecules of Examples 6-9 are all vertically aligned, and the stability of their alignment ability is excellent. In particular, in Example 9, the total amount of the first additive molecule and the second additive molecule added is 0.7 parts by weight. In Example 9, the voltage holding ratio is 98.4%, and the A Vth value is −0.022 V. Accordingly, the voltage holding ratio and the stability of the alignment ability can be further improved by simultaneously using the first additive molecule and the second additive molecule.

Referring to Examples 10-12 of Table 6, each of Examples 10-12 includes one of the first additive molecules and the compound represented by formula (V), and the compound represented by formula (V) includes one polymerizable group at the end of the molecule. The results show that the liquid-crystal molecules of Examples 10-12 are all vertically aligned, and the stability of their alignment ability is excellent. In particular, in Example 10, the total amount of the first additive molecule that is added and the compound represented by formula (V) is 0.7 parts by weight. In Example 10, the voltage holding ratio is 98.0%, and the ΔVth value is −0.010 V. In Example 11, the voltage holding ratio is 96.9%, and the ΔVth value is −0.050 V. Accordingly, the voltage holding ratio and the stability of the alignment ability can also be further improved by simultaneously using the first additive molecule and the compound represented by formula (V) having the polymerizable group.

In summary, the additive molecule of the present disclosure can have excellent vertical alignment ability while having a high voltage holding ratio. By adding the above-mentioned additive molecule to the liquid-crystal composition, it is possible to realize a state in which most of the liquid-crystal molecules are vertically aligned well without using a conventional alignment film. In order to balance the voltage holding ratio and the stability of the alignment ability of the liquid-crystal composition, the content of the first additive molecule and/or the second additive molecule may be adjusted. Furthermore, the liquid-crystal display device using the additive molecules of the embodiments of the present disclosure can have a high voltage retention rate (for example, the voltage retention rate greater than 80%) and excellent stability of the alignment ability. As a result, the performance and durability of the liquid-crystal display device can be significantly improved.

Although the disclosure has been described by way of example and in terms of the preferred embodiments, it should be understood that various modifications and similar arrangements (as would be apparent to those skilled in the art) can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims. 

What is claimed is:
 1. An additive comprising an additive molecule having a structure represented by formula (I):

wherein, in formula (I), R¹ represents fluorine, chlorine, hydrogen, a C₁-C₂₀ linear alkyl group, a C₃-C₂₀ branched alkyl group, a C₁-C₂₀ linear alkoxy group, or a C₃-C₂₀ branched alkoxy group, wherein the C₁-C₂₀ linear alkyl group, the C₃-C₂₀ branched alkyl group, the C₁-C₂₀ linear alkoxy group, or the C₃-C₂₀ branched alkoxy group is unsubstituted or at least one —CH₂— of the C₁-C₂₀ linear alkyl group, the C₃-C₂₀ branched alkyl group, the C₁-C₂₀ linear alkoxy group, or the C₃-C₂₀ branched alkoxy group is substituted by —C≡C—, —CH═CH—, —CF₂O—, —O—, —COO—, —OCO—, or —OOC—, and/or at least one hydrogen atom of the C₁-C₂₀ linear alkyl group, the C₃-C₂₀ branched alkyl group, the C₁-C₂₀ linear alkoxy group, or the C₃-C₂₀ branched alkoxy group is substituted by a halogen atom; A¹ represents a 1,4-phenylene group, a 1,4-cyclohexylene group, a benzofuran-2,5-diyl group, a 1,3-dioxane-2,5-diyl group, a tetrahydropyran-2,5-diyl group, a divalent dioxabicyclo[2.2.2]octylene group, a divalent trioxabicyclo[2.2.2]octylene group, a tetrahydronaphthalene-2,6-diyl group, a 1,3-cyclopentylene, a 1,3-cyclobutylene, or an indane-2,5-diyl group, wherein the 1,4-phenylene group, the 1,4-cyclohexylene group, the tetrahydronaphthalene-2,6-diyl group, the 1,3-cyclopentylene, the 1,3-cyclobutylene, or the indane-2,5-diyl group is unsubstituted or at least one hydrogen atom of the 1,4-phenylene group, the 1,4-cyclohexylene group, the tetrahydronaphthalene-2,6-diyl group, the 1,3-cyclopentylene, the 1,3-cyclobutylene, or the indane-2,5-diyl group is substituted by a halogen atom, —CH₃, —CH₂CH₃, or a —CN group, and/or at least one —CH₂— of the 1,4-phenylene group, the 1,4-cyclohexylene group, the tetrahydronaphthalene-2,6-diyl group, the 1,3-cyclopentylene, the 1,3-cyclobutylene, or the indane-2,5-diyl group is substituted by —O—, —N— or —S—, and wherein the —O—, —N—, and —S— do not directly bond to one another; A² represents a 1,4-phenylene group, a 1,4-cyclohexylene group, a benzofuran-2,5-diyl group, or an indane-2,5-diyl group, wherein the 1,4-phenylene group, the 1,4-cyclohexylene group, the benzofuran-2,5-diyl group, or the indane-2,5-diyl group is unsubstituted or at least one hydrogen atom of the 1,4-phenylene group, the 1,4-cyclohexylene group, the benzofuran-2,5-diyl group, or the indane-2,5-diyl group is substituted by a halogen atom, —CH₃, —CH₂CH₃, or a —CN group, and/or at least one —CH₂— of the 1,4-phenylene group, the 1,4-cyclohexylene group, the benzofuran-2,5-diyl group, or the indane-2,5-diyl group is substituted by —O—, —N— or —S—, and wherein the —O—, —N—, and —S— do not directly bond to one another; Z¹ represents a single bond, a C₁-C₁₅ alkylene group, a C₁-C₁₅ alkyleneoxy group, —C≡C—, —CH═CH—, —CF₂O—, —OCF₂—, —COO—, —OCO—, —OOC—, —CF₂—CF₂—, or —CF═CF—; n¹ represents 1, 2, or 3, and when n¹ represents 2 or 3, the two or more A¹ groups are identical to each other or different from each other, and the two or more Z¹ groups are identical to each other or different from each other; n² represents 0 or 1; and K¹ represents a structure represented by formula (Ia), formula (Ib), or formula (Ic):

wherein, in formula (Ia), formula (Ib), and formula (Ic), each of L¹, L², and L³ independently represents a single bond, a C₁-C₁₅ linear alkylene group, a C₃-C₁₅ branched alkylene group, a C₁-C₁₅ linear alkyleneoxy group, or a C₃-C₁₅ branched alkyleneoxy group, wherein the C₁-C₁₅ linear alkylene group, the C₃-C₁₅ branched alkylene group, the C₁-C₁₅ linear alkyleneoxy group, or the C₃-C₁₅ branched alkyleneoxy group is unsubstituted or at least one —CH₂— of the C₁-C₁₅ linear alkylene group, the C₃-C₁₅ branched alkylene group, the C₁-C₁₅ linear alkyleneoxy group, or the C₃-C₁₅ branched alkyleneoxy group is substituted by —C ≡C—, —CH═CH—, —CF₂O—, —SiR^(a) ₂—, —O—, —COO—, —OCO—, or —OOC—, and/or at least one hydrogen atom of the C₁-C₁₅ linear alkylene group, the C₃-C₁₅ branched alkylene group, the C₁-C₁₅ linear alkyleneoxy group, or the C₃-C₁₅ branched alkyleneoxy group is substituted by a halogen atom, and wherein R^(a) represents a C₁-C₁₀ linear alkyl group or a C₃-C₁₀ branched alkyl group, and two R^(a) groups bonded to the same Si atom are identical to each other or different from each other; each of R², R³ and R⁴ independently represents fluorine, chlorine, hydrogen, a C₁-C₁₀ linear alkyl group, a C₃-C₁₀ branched alkyl group, a C₁-C₁₀ linear alkoxy group, or a C₃-C₁₀ branched alkoxy group, wherein the C₁-C₁₀ linear alkyl group, the C₃-C₁₀ branched alkyl group, the C₁-C₁₀ linear alkoxy group, or the C₃-C₁₀ branched alkoxy group is unsubstituted or at least one —CH₂— of the C₁-C₁₀ linear alkyl group, the C₃-C₁₀ branched alkyl group, the C₁-C₁₀ linear alkoxy group, or the C₃-C₁₀ branched alkoxy group is substituted by —C≡C—, —CH═CH—, —CF₂O—, —O—, —COO—, —OCO—, or —OOC—, and/or at least one hydrogen atom of the C₁-C₁₀ linear alkyl group, the C₃-C₁₀ branched alkyl group, the C₁-C₁₀ linear alkoxy group, or the C₃-C₁₀ branched alkoxy group is substituted by a halogen atom; each of X¹ and X² independently represents

wherein Y¹ represents —OH, a C₁-C₁₅ alkyl group, or a C₂-C₁₅ alkenyl group, and at least one hydrogen atom of the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is substituted by —OH; Y² represents hydrogen, halogen, a C₁-C₁₅ alkyl group, or a C₂-C₁₅ alkenyl group, wherein the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is unsubstituted or at least one hydrogen atom of the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is substituted by a halogen atom; Z² represents a single bond, a C₁-C₁₅ alkylene group, a C₁-C₁₅ alkyleneoxy group, —C≡C—, —CH═CH—, —CF₂O—, —OCF₂—, —COO—, —OCO—, —OOC—, —CF₂—CF₂—, or —CF═CF—; A³ represents a 1,4-phenylene group, a 1,4-cyclohexylene group, a benzofuran-2,5-diyl group, or an indane-2,5-diyl group, wherein the 1,4-phenylene group, the 1,4-cyclohexylene group, the benzofuran-2,5-diyl group, or the indane-2,5-diyl group is unsubstituted or at least one hydrogen atom of the 1,4-phenylene group, the 1,4-cyclohexylene group, the benzofuran-2,5-diyl group, or the indane-2,5-diyl group is substituted by a halogen atom, —CH₃, —CH₂CH₃, or a —CN group, and/or at least one —CH₂— of the 1,4-phenylene group, the 1,4-cyclohexylene group, the benzofuran-2,5-diyl group, or the indane-2,5-diyl group is substituted by —O—, —N— or —S—, and wherein the —O—, —N—, and —S— do not directly bond to one another; n³+n⁴=3, n⁴ represents 2 or 3, and the two or more L² groups are identical to each other or different from each other, and the two or more X¹ groups are identical to each other or different from each other; n⁵+n⁶=3, n⁶ represents 2 or 3, and the two or more L² groups are identical to each other or different from each other, and the two or more X² groups are identical to each other or different from each other; n⁷ represents 0, 1, or 2, and when n⁷ represents 2, the two K³ groups are identical to each other or different from each other; n⁸ represents 1 or 2, and when n⁸ represents 2, the two Z² groups are identical to each other or different from each other, the two A³ groups are identical to each other or different from each other, and the two K³ groups are identical to each other or different from each other; when n⁸ represents 1, n⁷ represents 2; when n⁸ represents 2, n⁷ in the A³ group directly bonded to the K² group represents 2, and n⁷ in the A³ group directly bonded to the Z² group represents 0, 1, or 2; and K² represents a structure represented by formula (Id), formula (Ie), or formula (If):

and K³ represents a structure represented by formula (Ig) or formula (Ih):

wherein, in formula (Id), formula (Ie), formula (If), formula (Ig), and formula (Ih), each of L¹, L², L³, L⁴, L⁵, L⁶, and L⁷ independently represents a single bond, a C₁-C₁₅ linear alkylene group, a C₃-C₁₅ branched alkylene group, a C₁-C₁₅ linear alkyleneoxy group, or a C₃-C₁₅ branched alkyleneoxy group, wherein the C₁-C₁₅ linear alkylene group, the C₃-C₁₅ branched alkylene group, the C₁-C₁₅ linear alkyleneoxy group, or the C₃-C₁₅ branched alkyleneoxy group is unsubstituted or at least one —CH₂— of the C₁-C₁₅ linear alkylene group, the C₃-C₁₅ branched alkylene group, the C₁-C₁₅ linear alkyleneoxy group, or the C₃-C₁₅ branched alkyleneoxy group is substituted by —C≡C—, —CH═CH—, —CF₂O—, —SiR^(a) ₂—, —O—, —COO—, —OCO—, or —OOC—, and/or at least one hydrogen atom of the C₁-C₁₅ linear alkylene group, the C₃-C₁₅ branched alkylene group, the C₁-C₁₅ linear alkyleneoxy group, or the C₃-C₁₅ branched alkyleneoxy group is substituted by a halogen atom, and wherein R^(a) represents a C₁-C₁₀ linear alkyl group or a C₃-C₁₀ branched alkyl group, and two R^(a) groups bonded to the same Si atom are identical to each other or different from each other; each of R², R³, R⁴, R⁵ and R⁶ independently represents fluorine, chlorine, hydrogen, a C₁-C₁₀ linear alkyl group, a C₃-C₁₀ branched alkyl group, a C₁-C₁₀ linear alkoxy group, or a C₃-C₁₀ branched alkoxy group, wherein the C₁-C₁₀ linear alkyl group, the C₃-C₁₀ branched alkyl group, the C₁-C₁₀ linear alkoxy group, or the C₃-C₁₀ branched alkoxy group is unsubstituted or at least one —CH₂— of the C₁-C₁₀ linear alkyl group, the C₃-C₁₀ branched alkyl group, the C₁-C₁₀ linear alkoxy group, or the C₃-C₁₀ branched alkoxy group is substituted by —C≡C—, —CH═CH—, —CF₂O—, —O—, —COO—, —OCO—, or —OOC—, and/or at least one hydrogen atom of the C₁-C₁₀ linear alkyl group, the C₃-C₁₀ branched alkyl group, the C₁-C₁₀ linear alkoxy group, or the C₃-C₀ branched alkoxy group is substituted by a halogen atom; each of X³, X⁴, X⁵ and X⁶ independently represents hydrogen, —OH,

and at least one of X³, X⁴, X⁵ and X⁶ represents

wherein Y¹ represents —OH, a C₁-C₁₅ alkyl group, or a C₂-C₁₅ alkenyl group, and at least one hydrogen atom of the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is substituted by —OH; Y² represents hydrogen, halogen, a C₁-C₁₅ alkyl group, or a C₂-C₁₅ alkenyl group, wherein the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is unsubstituted or at least one hydrogen atom of the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is substituted by a halogen atom; n⁹+n¹⁰=3, n¹⁰ represents 2 or 3, and the two or more L⁷ groups are identical to each other or different from each other, and the two or more X⁴ groups are identical to each other or different from each other; n¹² represents 1, 2, or 3, n¹¹+n¹²=3, and when n¹² represents 2 or 3, the two or more L² groups are identical to each other or different from each other, and the two or more X⁵ groups are identical to each other or different from each other; when n¹¹ represents 2, the two R² groups are identical to each other or different from each other; and n¹⁴ represents 1, 2, or 3, n¹³+n¹⁴=3, and when n¹⁴ represents 2 or 3, the two or more L² groups are identical to each other or different from each other, and the two or more X⁶ groups are identical to each other or different from each other; when n¹³ represents 2, the two R⁴ groups are identical to each other or different from each other; and when X⁵ or X⁶ represents

K² represents -L⁴-R⁵.
 2. The additive as claimed in claim 1, wherein the additive molecule has a structure represented by formula (I):

wherein, in formula (I), R¹ represents fluorine, chlorine, hydrogen, a C₁-C₁₅ linear alkyl group, a C₃-C₁₅ branched alkyl group, a C₁-C₁₅ linear alkoxy group, or a C₃-C₁₅ branched alkoxy group, wherein the C₁-C₁₅ linear alkyl group, the C₃-C₁₅ branched alkyl group, the C₁-C₁₅ linear alkoxy group, or the C₃-C₁₅ branched alkoxy group is unsubstituted or at least one —CH₂— of the C₁-C₁₅ linear alkyl group, the C₃-C₁₅ branched alkyl group, the C₁-C₁₅ linear alkoxy group, or the C₃-C₁₅ branched alkoxy group is substituted by —CH═CH—, —CF₂O—, —O—, —COO—, —OCO—, or —OOC—, and/or at least one hydrogen atom of the C₁-C₁₅ linear alkyl group, the C₃-C₁₅ branched alkyl group, the C₁-C₁₅ linear alkoxy group, or the C₃-C₁₅ branched alkoxy group is substituted by a halogen atom; the definitions of A¹, A², Z¹, n¹, and n² are respectively the same as the definitions of A¹, A², Z¹, n¹, and n² defined in claim 1; and K¹ represents a structure represented by formula (I′a), formula (I′b), or formula (I′c):

wherein, in formula (I′a), formula (I′b), and formula (I′c), the definitions of L², L³, n³, n⁴, n⁵, and n⁶ are respectively the same as the definitions of L², L³, n³, n⁴, n⁵, and n⁶ defined in claim 1; each of R², R³ and R⁴ independently represents fluorine, chlorine, hydrogen, a C₁-C₈ linear alkyl group, a C₃-C₈ branched alkyl group, a C₁-C₈ linear alkoxy group, or a C₃-C₈ branched alkoxy group, wherein the C₁-C₈ linear alkyl group, the C₃-C₈ branched alkyl group, the C₁-C₈ linear alkoxy group, or the C₃-C₈ branched alkoxy group is unsubstituted or at least one —CH₂— of the C₁-C₈ linear alkyl group, the C₃-C₈ branched alkyl group, the C₁-C₈ linear alkoxy group, or the C₃-C₈ branched alkoxy group is substituted by —CH═CH—, —CF₂O—, —O—, —COO—, —OCO—, or —OOC—, and/or at least one hydrogen atom of the C₁-C₈ linear alkyl group, the C₃-C₈ branched alkyl group, the C₁-C₈ linear alkoxy group, or the C₃-C₈ branched alkoxy group is substituted by a halogen atom; each of X¹ and X² independently represents

wherein Y¹ represents —OH, a C₁-C₈ alkyl group, or a C₂-C₈ alkenyl group, and at least one hydrogen atom of the C₁-C₈ alkyl group or the C₂-C₈ alkenyl group is substituted by —OH; Y² represents hydrogen, halogen, a C₁-C₈ alkyl group, or a C₂-C₈ alkenyl group, wherein the C₁-C₈ alkyl group or the C₂-C₈ alkenyl group is unsubstituted or at least one hydrogen atom of the C₁-C₈ alkyl group or the C₂-C₈ alkenyl group is substituted by a halogen atom; K² represents a structure represented by formula (Id), formula (Ie), or formula (If):

and K³ represents a structure represented by formula (Ig) or formula (Ih):

wherein, in formula (Id), formula (Ie), formula (If), formula (Ig), and formula (Ih), the definitions of L¹, L², L³, L⁴, L⁵, L⁶, L⁷, n n¹⁰, n¹¹ n¹², n¹³, and n¹⁴ are respectively the same as the definitions of L¹, L², L³, L⁴, L⁵, L⁶, L⁷, n⁹ n, n¹⁰, n¹¹, n¹², n¹³, and n¹⁴ defined in claim 1; each of R², R³, R⁴, R⁵ and R⁶ independently represents fluorine, chlorine, hydrogen, a C₁-C₈ linear alkyl group, a C₃-C₈ branched alkyl group, a C₁-C₈ linear alkoxy group, or a C₃-C₈ branched alkoxy group, wherein the C₁-C₈ linear alkyl group, the C₃-C₈ branched alkyl group, the C₁-C₈ linear alkoxy group, or the C₃-C₈ branched alkoxy group is unsubstituted or at least one —CH₂— of the C₁-C₈ linear alkyl group, the C₃-C₈ branched alkyl group, the C₁-C₈ linear alkoxy group, or the C₃-C₈ branched alkoxy group is substituted by —CH═CH—, —CF₂O—, —O—, —COO—, —OCO—, or —OOC—, and/or at least one hydrogen atom of the C₁-C₈ linear alkyl group, the C₃-C₈ branched alkyl group, the C₁-C₈ linear alkoxy group, or the C₃-C₈ branched alkoxy group is substituted by a halogen atom; each of X³, X⁴, X⁵ and X⁶ independently represents hydrogen, —OH,

wherein Y¹ represents —OH, a C₁-C₈ alkyl group, or a C₂-C₈ alkenyl group, and at least one hydrogen atom of the C₁-C₈ alkyl group or the C₂-C₈ alkenyl group is substituted by —OH; Y² represents hydrogen, halogen, a C₁-C₈ alkyl group, or a C₂-C₈ alkenyl group, wherein the C₁-C₈ alkyl group or the C₂-C₈ alkenyl group is unsubstituted or at least one hydrogen atom of the C₁-C₈ alkyl group or the C₂-C₈ alkenyl group is substituted by a halogen atom; wherein at least one of X³, X⁴, X⁵ and X⁶ represents

and when X⁵ or X⁶ represents

K² represents -L⁴-R⁵.
 3. The additive as claimed in claim 2, wherein the additive molecule comprises a first additive molecule, and the first additive molecule has a structure represented by formula (I):

wherein, in formula (I), the definitions of R¹, A¹, A², Z¹, n¹, and n² are respectively the same as the definitions of R¹, A¹, A², Z¹, n¹, and n² defined in claim 2; and K¹ represents a structure represented by formula (I′a), formula (I′b), or formula (I′c):

wherein, in formula (I′a), formula (I′b), and formula (I′c), the definitions of L², L³, R², R³, R⁴, n³, n⁴, n⁵, and n⁶ are respectively the same as the definitions of L², L³, R², R³, R⁴, n³, n⁴, n⁵, and n⁶ defined in claim 2; each of X¹ and X² independently represents

and the definitions of Y¹ and Y² are respectively the same as the definitions of Y¹ and Y² defined in claim 2; K² represents a structure represented by formula (Id), formula (Ie), or formula (If):

and K³ represents a structure represented by formula (Ig) or formula (Ih):

wherein, in formula (Id), formula (Ie), formula (If), formula (Ig), and formula (Ih), the definitions of L¹, L², L³, L⁴, L⁵, L⁶, L⁷, R², R³, R⁴, R⁵, R⁶, n⁹, n¹⁰, n¹¹, n¹² n¹³, and n¹⁴ are respectively the same as the definitions of L¹, L², L³, L⁴, L⁵, L⁶, L⁷, R², R³, R⁴, R⁵, R⁶, n⁹, n¹⁰, n¹¹, n¹², n¹³, and n¹⁴ defined in claim 2; each of X³, X⁴, X⁵ and X⁶ independently represents hydrogen, —OH,

and the definitions of Y¹ and Y² are respectively the same as the definitions of Y¹ and Y² defined in claim 2; when K¹ represents the structure represented by formula (I′a) or formula (I′b), at least one of X¹ and X² represents

when K¹ represents the structure represented by formula (I′c), and K² represents the structure represented by formula (Id), at least one of X⁵ and X⁶ represents,

when K¹ represents the structure represented by formula (I′c), and K² represents the structure represented by formula (Ie) or formula (If), at least one of X³, X⁴, X⁵ and X⁶ represents


4. The additive as claimed in claim 3, wherein the additive molecule further comprises a second additive molecule, and the second additive molecule has a structure represented by formula (I):

wherein, in formula (I), the definitions of R¹, A¹, A², Z¹, n¹, and n² are respectively the same as the definitions of R¹, A¹, A², Z¹, n¹, and n² defined in claim 2; and K¹ represents a structure represented by formula (I′a), formula (I′b), or formula (I′c):

wherein, in formula (I′a), formula (I′b), and formula (I′c), the definitions of L², L³, R², R³, R⁴, n³, n⁴, n⁵, and n⁶ are respectively the same as the definitions of L², L³, R², R³, R⁴, n³, n⁴, n⁵, and n⁶ defined in claim 2; each of X¹ and X² independently represents

and the definitions of Y¹ and Y² are respectively the same as the definitions of Y¹ and Y² defined in claim 2; K² represents a structure represented by formula (Id), formula (Ie), or formula (If):

and K³ represents a structure represented by formula (Ig) or formula (Ih):

wherein, in formula (Id), formula (Ie), formula (If), formula (Ig), and formula (Ih), the definitions of L¹, L², L³, L⁴, L⁵, L⁶, L⁷, R², R³, R⁴, R⁵, R⁶, n⁹, n¹⁰, n¹¹, n¹², n¹³, and n¹⁴ are respectively the same as the definitions of L¹, L², L³, L⁴, L⁵, L⁶, L⁷, R², R³, R⁴, R⁵, R⁶, n⁹, n¹⁰, n¹¹, n¹², n¹³, and n¹⁴ defined in claim 2; each of X³, X⁴, X⁵ and X⁶ independently represents hydrogen, —OH,

and the definitions of Y¹ and Y² are respectively the same as the definitions of Y¹ and Y² defined in claim 2; when K¹ represents the structure represented by formula (I′a) or formula (I′b), each of X¹ and X² independently represents

when K¹ represents the structure represented by formula (I′ c), each of X³, X⁴, X⁵ and X⁶ independently represents hydrogen or


5. The additive as claimed in claim 4, wherein when the amount of the first additive molecule is set to 1 part by weight, the amount of the second additive molecule is 0.1-60 parts by weight.
 6. The additive as claimed in claim 2, wherein the additive molecule comprises a second additive molecule, and the second additive molecule has a structure represented by formula (I):

wherein, in formula (I), the definitions of R¹, A¹, A², Z¹, n¹, and n² are respectively the same as the definitions of R¹, A¹, A², Z¹, n¹, and n² defined in claim 2; and K¹ represents a structure represented by formula (I′a), formula (I′b), or formula (I′c):

wherein, in formula (I′a), formula (I′b), and formula (I′c), the definitions of L², L³, R², R³, R⁴, n³, n⁴, n⁵, and n⁶ are respectively the same as the definitions of L², L³, R², R³, R⁴, n³, n⁴, n⁵, and n⁶ defined in claim 2; each of X¹ and X² independently represents

and the definitions of Y¹ and Y² are respectively the same as the definitions of Y¹ and Y² defined in claim 2; K² represents a structure represented by formula (Id), formula (Ie), or formula (If):

and K³ represents a structure represented by formula (Ig) or formula (Ih):

wherein, in formula (Id), formula (Ie), formula (If), formula (Ig), and formula (Ih), the definitions of L¹, L², L³, L⁴, L⁵, L⁶, L⁷, R², R³, R⁴, R⁵, R⁶, n⁹, n¹⁰, n¹¹, n¹² n¹³, and n¹⁴ are respectively the same as the definitions of L¹, L², L³, L⁴, L⁵, L⁶, L⁷, R², R³, R⁴, R⁵, R⁶, n⁹, n¹⁰, n¹¹, n¹², n¹³, and n¹⁴ defined in claim 2; each of X³, X⁴, X⁵ and X⁶ independently represents hydrogen, —OH,

and the definitions of Y¹ and Y² are respectively the same as the definitions of Y¹ and Y² defined in claim 2; when K¹ represents the structure represented by formula (I′a) or formula (I′b), each of X¹ and X² independently represents

when K¹ represents the structure represented by formula (I′ c), each of X³, X⁴, X⁵ and X⁶ independently represents hydrogen or


7. A liquid-crystal composition, comprising a first component and a second component, wherein the first component comprises at least one additive as claimed in claim 1, and the second component comprises at least one compound represented by formula (II):

wherein each of R²¹ and R²² independently represents hydrogen, halogen, a C₁-C₁₅ alkyl group, or a C₂-C₁₅ alkenyl group, wherein the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is unsubstituted or at least one hydrogen atom of the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is substituted by a halogen atom, and/or at least one —CH₂— of the C₁-C₁₅ alkyl group or the C₂-C₁₅ alkenyl group is substituted by —O—, and wherein the —O— does not directly bond to another —O—; each of B¹, B², and B³ independently represents a 1,4-phenylene group, a 1,4-cyclohexylene group, a benzofuran-2,5-diyl group, a 1,3-dioxane-2,5-diyl group, a tetrahydropyran-2,5-diyl group, a divalent dioxabicyclo[2.2.2]octylene group, a divalent trioxabicyclo[2.2.2]octylene group, a tetrahydronaphthalene-2,6-diyl group, or an indane-2,5-diyl group, wherein the 1,4-phenylene group, the 1,4-cyclohexylene group, the 1,3-dioxane-2,5-diyl group, the benzofuran-2,5-diyl group, the tetrahydronaphthalene-2,6-diyl group, the indane-2,5-diyl group, or the tetrahydropyran-2,5-diyl group is unsubstituted or at least one hydrogen atom of the 1,4-phenylene group, the 1,4-cyclohexylene group, the 1,3-dioxane-2,5-diyl group, the benzofuran-2,5-diyl group, the tetrahydronaphthalene-2,6-diyl group, the indane-2,5-diyl group, or the tetrahydropyran-2,5-diyl group is substituted by a halogen atom or a —CN group, and/or at least one —CH₂— of the 1,4-phenylene group, the 1,4-cyclohexylene group, the 1,3-dioxane-2,5-diyl group, the benzofuran-2,5-diyl group, the tetrahydronaphthalene-2,6-diyl group, the indane-2,5-diyl group, or the tetrahydropyran-2,5-diyl group is substituted by —O—, —N— or —S—, and wherein the —O—, —N—, and —S— do not directly bond to one another; each of Z²¹ and Z²² independently represents a single bond, a C₁-C₄ alkylene group, a C₂-C₄ alkenylene group, or a C₂-C₄ alkynylene group, wherein the C₁-C₄ alkylene group, the C₂-C₄ alkenylene group, or the C₂-C₄ alkynylene group is unsubstituted or at least one hydrogen atom of the C₁-C₄ alkylene group, the C₂-C₄ alkenylene group, or the C₂-C₄ alkynylene group is substituted by a halogen atom or a —CN group, and/or at least one —CH₂— of the C₁-C₄ alkylene group, the C₂-C₄ alkenylene group, or the C₂-C₄ alkynylene group is substituted by —O— or —S—, and wherein the —O— does not directly bond to —O— or —S—, and —S— does not directly bond to —S—; and n²¹ represents 0, 1, or 2, and when n²¹ represents 2, the two B¹ groups are identical to each other or different from each other.
 8. The liquid-crystal composition as claimed in claim 7, wherein the second component comprises at least one compound represented by formula (II-1) or formula (II-2):

wherein the definitions of R²¹, R²², B¹, B², Z²², and n²¹ are respectively the same as the definitions of R²¹, R²², B¹, B², Z²², and n²¹ defined in claim
 7. 9. The liquid-crystal composition as claimed in claim 7, wherein when a total weight of the second component is 100 parts by weight, the first component is 0.01-parts by weight.
 10. The liquid-crystal composition as claimed in claim 7, further comprising a third component, wherein the third component comprises at least one compound represented by formula (III), formula (IV), or formula (V):

wherein each of K²¹, K²², K²³, and K²⁴ independently represents hydrogen or a methyl group; each of Z²³ and Z²⁴ independently represents a single bond, a C₁-C₁₅ linear alkylene group, a C₃-C₁₅ branched alkylene group, a C₂-C₁₅ linear alkenylene group, or a C₃-C₁₅ branched alkenylene group, wherein the C₁-C₁₅ linear alkylene group, the C₃-C₁₅ branched alkylene group, the C₂-C₁₅ linear alkenylene group, or the C₃-C₁₅ branched alkenylene group is unsubstituted or at least one hydrogen atom of the C₁-C₁₅ linear alkylene group, the C₃-C₁₅ branched alkylene group, the C₂-C₁₅ linear alkenylene group, or the C₃-C₁₅ branched alkenylene group is substituted by a halogen atom, and/or at least one —CH₂— of the C₁-C₁₅ linear alkylene group, the C₃-C₁₅ branched alkylene group, the C₂-C₁₅ linear alkenylene group, or the C₃-C₁₅ branched alkenylene group is substituted by —O—, —CO—, —COO—, or —OCO—, and wherein the —O—, —CO—, —COO—, and —OCO— do not directly bond to one another; each of Z²⁵, Z²⁶, Z²⁷, and Z²⁸ independently represents a single bond, —C≡C—, a C₁-C₁₅ linear alkylene group, a C₃-C₁₅ branched alkylene group, a C₂-C₁₅ linear alkenylene group, or a C₃-C₁₅ branched alkenylene group, wherein the C₁-C₁₅ linear alkylene group, the C₃-C₅ branched alkylene group, the C₂-C₁₅ linear alkenylene group, or the C₃-C₁₅ branched alkenylene group is unsubstituted or at least one hydrogen atom of the C₁-C₁₅ linear alkylene group, the C₃-C₁₅ branched alkylene group, the C₂-C₁₅ linear alkenylene group, or the C₃-C₁₅ branched alkenylene group is substituted by a halogen atom, and/or at least one —CH₂— of the C₁-C₁₅ linear alkylene group, the C₃-C₁₅ branched alkylene group, the C₂-C₁₅ linear alkenylene group, or the C₃-C₁₅ branched alkenylene group is substituted by —SiR^(e) ₂—, —S—, —O—, —CO—, —COO—, —OCO—, —CO—NR^(e)—, or —NR^(e)—CO—, and the —SiR^(e) ₂—, —S—, —O—, —CO—, —COO—, —OCO—, —CO—NR^(e)—, and —NR^(e)—CO— do not directly bond to one another, wherein R^(e) represents hydrogen, a C₁-C₄ linear alkyl group, or a C₃-C₄ branched alkyl group, and the two R^(e) groups bonded to the same Si atom are identical to each other or different from each other; each of B⁴, B⁵, B⁶ and B⁷ independently represents a 1,4-phenylene group, a 1,4-cyclohexylene group, a benzofuran-2,5-diyl group, a 1,3-dioxane-2,5-diyl group, a tetrahydropyran-2,5-diyl group, a divalent dioxabicyclo[2.2.2]octylene group, a divalent trioxabicyclo[2.2.2]octylene group, a tetrahydronaphthalene-2,6-diyl group, or an indane-2,5-diyl group, wherein the 1,4-phenylene group, the 1,4-cyclohexylene group, the benzofuran-2,5-diyl group, the 1,3-dioxane-2,5-diyl group, the tetrahydropyran-2,5-diyl group, the divalent dioxabicyclo[2.2.2]octylene group, the divalent trioxabicyclo[2.2.2]octylene group, the tetrahydronaphthalene-2,6-diyl group, or the indane-2,5-diyl group is unsubstituted or is substituted by at least one substituent, wherein the at least one substituent is selected from fluorine, chlorine, a —CN group, a C₁-C₁₂ linear alkyl group, a C₃-C₁₂ branched alkyl group, a C₂-C₁₂ linear alkenyl group, a C₂-C₁₂ linear alkynyl group, a C₄-C₁₂ branched alkenyl group, or a C₄-C₁₂ branched alkynyl group, wherein the C₁-C₁₂ linear alkyl group, the C₃-C₁₂ branched alkyl group, the C₂-C₁₂ linear alkenyl group, the C₂-C₁₂ linear alkynyl group, the C₄-C₁₂ branched alkenyl group, or the C₄-C₁₂ branched alkynyl group is unsubstituted or at least one hydrogen atom of the C₁-C₁₂ linear alkyl group, the C₃-C₁₂ branched alkyl group, the C₂-C₁₂ linear alkenyl group, the C₂-C₁₂ linear alkynyl group, the C₄-C₁₂ branched alkenyl group, or the C₄-C₁₂ branched alkynyl group is substituted by a halogen atom, and/or at least one —CH₂— of the C₁-C₁₂ linear alkyl group, the C₃-C₁₂ branched alkyl group, the C₂-C₁₂ linear alkenyl group, the C₂-C₁₂ linear alkynyl group, the C₄-C₁₂ branched alkenyl group, or the C₄-C₁₂ branched alkynyl group is substituted by —O—, —CO—, —COO—, or —OCO—, and the —O—, —CO—, —COO—, and —OCO— do not directly bond to one another; M¹ represents a single bond, —CH₂O—, —OCH₂—, —CH₂CH₂—, —CH═CH—, —C≡C—, —CH₂—, —C(CH₃)₂—, —C(CF₃)₂—, —SiH₂—, —Si(CH₃)₂—, or —Si(CF₃)₂—; each of R²³ and R²⁴ independently represents a C₁-C₃₀ linear alkyl group or a C₃-C₃₀ branched alkyl group, wherein the C₁-C₃₀ linear alkyl group or the C₃-C₃₀ branched alkyl group is unsubstituted or at least one hydrogen atom of the C₁-C₃₀ linear alkyl group or the C₃-C₃₀ branched alkyl group is substituted by a halogen atom, and/or at least one —CH₂— of the C₁-C₃₀ linear alkyl group or the C₃-C₃₀ branched alkyl group is substituted by —Si—, —O—, —CO—, —COO—, or —OCO—, and the —Si—, —O—, —CO—, —COO—, and —OCO— do not directly bond to one another; and each of n²² and n²³ independently represents an integer of 0 to 3, and when n²² is 2 or more, the two or more B⁴ groups are identical to each other or different from each other, and the two or more M¹ groups are identical to each other or different from each other; and when n²³ is 2 or more, the two or more B⁶ groups are identical to each other or different from each other, and the two or more Z²⁷ groups are identical to each other or different from each other.
 11. The liquid-crystal composition as claimed in claim 10, wherein when a total weight of the second component is 100 parts by weight, the third component is 0.01-10 parts by weight.
 12. A liquid-crystal display device comprising: a first substrate; a second substrate disposed opposite to the first substrate; a liquid-crystal layer disposed between the first substrate and the second substrate, wherein the liquid-crystal layer comprises the additive as claimed in claim
 1. 